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patches: Add fix for -Wshift-count-overflow in drivers/dma/mmp_pdma.c
Link: ClangBuiltLinux/linux#2122 Signed-off-by: Nathan Chancellor <[email protected]>
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‎patches/mainline/20250918_guodong_dmaengine_mmp_pdma_fix_dma_mask_handling.patch‎

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From git@z Thu Jan 1 00:00:00 1970
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Subject: [PATCH] dmaengine: mmp_pdma: fix DMA mask handling
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From: Guodong Xu <[email protected]>
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Date: Thu, 18 Sep 2025 22:27:27 +0800
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Message-Id: <20250918-mmp-pdma-simplify-dma-addressing-v1-1-5c2be2b85696@riscstar.com>
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MIME-Version: 1.0
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Content-Type: text/plain; charset="utf-8"
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Content-Transfer-Encoding: 7bit
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The driver's existing logic for setting the DMA mask for "marvell,pdma-1.0"
11+
was flawed. It incorrectly relied on pdev->dev->coherent_dma_mask instead
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of declaring the hardware's fixed addressing capability. A cleaner and
13+
more correct approach is to define the mask directly based on the hardware
14+
limitations.
15+
16+
The MMP/PXA PDMA controller is a 32-bit DMA engine. This is supported by
17+
datasheets and various dtsi files for PXA25x, PXA27x, PXA3xx, and MMP2,
18+
all of which are 32-bit systems.
19+
20+
This patch simplifies the driver's logic by replacing the 'u64 dma_mask'
21+
field with a simpler 'u32 dma_width' to store the addressing capability
22+
in bits. The complex if/else block in probe() is then replaced with a
23+
single, clear call to dma_set_mask_and_coherent(). This sets a fixed
24+
32-bit DMA mask for "marvell,pdma-1.0" and a 64-bit mask for
25+
"spacemit,k1-pdma," matching each device's hardware capabilities.
26+
27+
Finally, this change also works around a specific build error encountered
28+
with clang-20 on x86_64 allyesconfig. The shift-count-overflow error is
29+
caused by a known clang compiler issue where the DMA_BIT_MASK(n) macro's
30+
ternary operator is not correctly evaluated in static initializers. By
31+
moving the macro's evaluation into the probe() function, the driver avoids
32+
this compiler bug.
33+
34+
Fixes: 5cfe585d8624 ("dmaengine: mmp_pdma: Add SpacemiT K1 PDMA support with 64-bit addressing")
35+
Reported-by: Naresh Kamboju <[email protected]>
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Closes: https://lore.kernel.org/lkml/CA+G9fYsPcMfW-e_0_TRqu4cnwqOqYF3aJOeKUYk6Z4qRStdFvg@mail.gmail.com
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Suggested-by: Arnd Bergmann <[email protected]>
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Signed-off-by: Guodong Xu <[email protected]>
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Tested-by: Naresh Kamboju <[email protected]>
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Tested-by: Nathan Chancellor <[email protected]> # build
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Reviewed-by: Arnd Bergmann <[email protected]>
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Link: https://patch.msgid.link/20250918-mmp-pdma-simplify-dma-addressing-v1-1-5c2be2b85696@riscstar.com
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---
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Hi Vinod, Arnd, and all,
45+
46+
This patch fixes a build failure in the mmp_pdma driver when using
47+
clang-20, as reported by Naresh Kamboju [1]. The error,
48+
a -Wshift-count-overflow warning, is caused by a known issue in the clang
49+
compiler. When the DMA_BIT_MASK(64) macro is used in a static initializer,
50+
it triggers a long-standing bug in how clang evaluates compile-time
51+
constants [2, 3]. Thanks to Nathan Chancellor for providing these links.
52+
53+
While investigating this, Arnd Bergmann pointed out that the driver's
54+
logic for setting the DMA mask was unnecessarily complex. This logic,
55+
which was inherited from the original Marvel PDMA driver when adding
56+
support for SpacemiT K1 DMA, could be simplified. A better solution is to
57+
set each device's DMA mask directly based on its hardware capability.
58+
59+
This patch implements Arnd's suggestion. It refactors the driver to store
60+
the controller's DMA width (either 32 or 64 bits) and generates the mask
61+
at runtime within the probe() function.
62+
63+
This approach also avoids the clang false error reporting.
64+
65+
This patch is based on dmaengine.git next [4].
66+
67+
Thanks,
68+
Guodong Xu
69+
70+
[1] https://lore.kernel.org/lkml/CA+G9fYsPcMfW-e_0_TRqu4cnwqOqYF3aJOeKUYk6Z4qRStdFvg@mail.gmail.com/
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[2] https://github.com/ClangBuiltLinux/linux/issues/92
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[3] https://github.com/llvm/llvm-project/issues/38137
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[4] https://git.kernel.org/pub/scm/linux/kernel/git/vkoul/dmaengine.git/log/?h=next
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---
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drivers/dma/mmp_pdma.c | 20 ++++++++------------
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1 file changed, 8 insertions(+), 12 deletions(-)
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diff --git a/drivers/dma/mmp_pdma.c b/drivers/dma/mmp_pdma.c
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index d07229a748868b8115892c63c54c16130d88e326..86661eb3cde1ff6d6d8f02b6f0d4142878b5a890 100644
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--- a/drivers/dma/mmp_pdma.c
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+++ b/drivers/dma/mmp_pdma.c
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@@ -152,8 +152,8 @@ struct mmp_pdma_phy {
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*
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* Controller Configuration:
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* @run_bits: Control bits in DCSR register for channel start/stop
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- * @dma_mask: DMA addressing capability of controller. 0 to use OF/platform
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- * settings, or explicit mask like DMA_BIT_MASK(32/64)
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+ * @dma_width: DMA addressing width in bits (32 or 64). Determines the
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+ * DMA mask capability of the controller hardware.
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*/
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struct mmp_pdma_ops {
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/* Hardware Register Operations */
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@@ -173,7 +173,7 @@ struct mmp_pdma_ops {
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/* Controller Configuration */
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u32 run_bits;
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- u64 dma_mask;
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+ u32 dma_width;
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};
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struct mmp_pdma_device {
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@@ -1172,7 +1172,7 @@ static const struct mmp_pdma_ops marvell_pdma_v1_ops = {
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.get_desc_src_addr = get_desc_src_addr_32,
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.get_desc_dst_addr = get_desc_dst_addr_32,
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.run_bits = (DCSR_RUN),
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- .dma_mask = 0, /* let OF/platform set DMA mask */
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+ .dma_width = 32,
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};
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static const struct mmp_pdma_ops spacemit_k1_pdma_ops = {
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@@ -1185,7 +1185,7 @@ static const struct mmp_pdma_ops spacemit_k1_pdma_ops = {
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.get_desc_src_addr = get_desc_src_addr_64,
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.get_desc_dst_addr = get_desc_dst_addr_64,
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.run_bits = (DCSR_RUN | DCSR_LPAEEN),
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- .dma_mask = DMA_BIT_MASK(64), /* force 64-bit DMA addr capability */
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+ .dma_width = 64,
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};
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static const struct of_device_id mmp_pdma_dt_ids[] = {
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@@ -1314,13 +1314,9 @@ static int mmp_pdma_probe(struct platform_device *op)
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pdev->device.directions = BIT(DMA_MEM_TO_DEV) | BIT(DMA_DEV_TO_MEM);
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pdev->device.residue_granularity = DMA_RESIDUE_GRANULARITY_DESCRIPTOR;
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- /* Set DMA mask based on ops->dma_mask, or OF/platform */
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- if (pdev->ops->dma_mask)
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- dma_set_mask(pdev->dev, pdev->ops->dma_mask);
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- else if (pdev->dev->coherent_dma_mask)
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- dma_set_mask(pdev->dev, pdev->dev->coherent_dma_mask);
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- else
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- dma_set_mask(pdev->dev, DMA_BIT_MASK(64));
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+ /* Set DMA mask based on controller hardware capabilities */
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+ dma_set_mask_and_coherent(pdev->dev,
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+ DMA_BIT_MASK(pdev->ops->dma_width));
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ret = dma_async_device_register(&pdev->device);
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if (ret) {
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---
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base-commit: cc0bacac6de7763a038550cf43cb94634d8be9cd
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change-id: 20250904-mmp-pdma-simplify-dma-addressing-f6aef03e07c3
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Best regards,
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--
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Guodong Xu <[email protected]>
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‎patches/mainline/series‎

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20250918_guodong_dmaengine_mmp_pdma_fix_dma_mask_handling.patch

‎patches/tip/20250918_guodong_dmaengine_mmp_pdma_fix_dma_mask_handling.patch‎

Lines changed: 145 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,145 @@
1+
From git@z Thu Jan 1 00:00:00 1970
2+
Subject: [PATCH] dmaengine: mmp_pdma: fix DMA mask handling
3+
From: Guodong Xu <[email protected]>
4+
Date: Thu, 18 Sep 2025 22:27:27 +0800
5+
Message-Id: <20250918-mmp-pdma-simplify-dma-addressing-v1-1-5c2be2b85696@riscstar.com>
6+
MIME-Version: 1.0
7+
Content-Type: text/plain; charset="utf-8"
8+
Content-Transfer-Encoding: 7bit
9+
10+
The driver's existing logic for setting the DMA mask for "marvell,pdma-1.0"
11+
was flawed. It incorrectly relied on pdev->dev->coherent_dma_mask instead
12+
of declaring the hardware's fixed addressing capability. A cleaner and
13+
more correct approach is to define the mask directly based on the hardware
14+
limitations.
15+
16+
The MMP/PXA PDMA controller is a 32-bit DMA engine. This is supported by
17+
datasheets and various dtsi files for PXA25x, PXA27x, PXA3xx, and MMP2,
18+
all of which are 32-bit systems.
19+
20+
This patch simplifies the driver's logic by replacing the 'u64 dma_mask'
21+
field with a simpler 'u32 dma_width' to store the addressing capability
22+
in bits. The complex if/else block in probe() is then replaced with a
23+
single, clear call to dma_set_mask_and_coherent(). This sets a fixed
24+
32-bit DMA mask for "marvell,pdma-1.0" and a 64-bit mask for
25+
"spacemit,k1-pdma," matching each device's hardware capabilities.
26+
27+
Finally, this change also works around a specific build error encountered
28+
with clang-20 on x86_64 allyesconfig. The shift-count-overflow error is
29+
caused by a known clang compiler issue where the DMA_BIT_MASK(n) macro's
30+
ternary operator is not correctly evaluated in static initializers. By
31+
moving the macro's evaluation into the probe() function, the driver avoids
32+
this compiler bug.
33+
34+
Fixes: 5cfe585d8624 ("dmaengine: mmp_pdma: Add SpacemiT K1 PDMA support with 64-bit addressing")
35+
Reported-by: Naresh Kamboju <[email protected]>
36+
Closes: https://lore.kernel.org/lkml/CA+G9fYsPcMfW-e_0_TRqu4cnwqOqYF3aJOeKUYk6Z4qRStdFvg@mail.gmail.com
37+
Suggested-by: Arnd Bergmann <[email protected]>
38+
Signed-off-by: Guodong Xu <[email protected]>
39+
Tested-by: Naresh Kamboju <[email protected]>
40+
Tested-by: Nathan Chancellor <[email protected]> # build
41+
Reviewed-by: Arnd Bergmann <[email protected]>
42+
Link: https://patch.msgid.link/20250918-mmp-pdma-simplify-dma-addressing-v1-1-5c2be2b85696@riscstar.com
43+
---
44+
Hi Vinod, Arnd, and all,
45+
46+
This patch fixes a build failure in the mmp_pdma driver when using
47+
clang-20, as reported by Naresh Kamboju [1]. The error,
48+
a -Wshift-count-overflow warning, is caused by a known issue in the clang
49+
compiler. When the DMA_BIT_MASK(64) macro is used in a static initializer,
50+
it triggers a long-standing bug in how clang evaluates compile-time
51+
constants [2, 3]. Thanks to Nathan Chancellor for providing these links.
52+
53+
While investigating this, Arnd Bergmann pointed out that the driver's
54+
logic for setting the DMA mask was unnecessarily complex. This logic,
55+
which was inherited from the original Marvel PDMA driver when adding
56+
support for SpacemiT K1 DMA, could be simplified. A better solution is to
57+
set each device's DMA mask directly based on its hardware capability.
58+
59+
This patch implements Arnd's suggestion. It refactors the driver to store
60+
the controller's DMA width (either 32 or 64 bits) and generates the mask
61+
at runtime within the probe() function.
62+
63+
This approach also avoids the clang false error reporting.
64+
65+
This patch is based on dmaengine.git next [4].
66+
67+
Thanks,
68+
Guodong Xu
69+
70+
[1] https://lore.kernel.org/lkml/CA+G9fYsPcMfW-e_0_TRqu4cnwqOqYF3aJOeKUYk6Z4qRStdFvg@mail.gmail.com/
71+
[2] https://github.com/ClangBuiltLinux/linux/issues/92
72+
[3] https://github.com/llvm/llvm-project/issues/38137
73+
[4] https://git.kernel.org/pub/scm/linux/kernel/git/vkoul/dmaengine.git/log/?h=next
74+
---
75+
drivers/dma/mmp_pdma.c | 20 ++++++++------------
76+
1 file changed, 8 insertions(+), 12 deletions(-)
77+
78+
diff --git a/drivers/dma/mmp_pdma.c b/drivers/dma/mmp_pdma.c
79+
index d07229a748868b8115892c63c54c16130d88e326..86661eb3cde1ff6d6d8f02b6f0d4142878b5a890 100644
80+
--- a/drivers/dma/mmp_pdma.c
81+
+++ b/drivers/dma/mmp_pdma.c
82+
@@ -152,8 +152,8 @@ struct mmp_pdma_phy {
83+
*
84+
* Controller Configuration:
85+
* @run_bits: Control bits in DCSR register for channel start/stop
86+
- * @dma_mask: DMA addressing capability of controller. 0 to use OF/platform
87+
- * settings, or explicit mask like DMA_BIT_MASK(32/64)
88+
+ * @dma_width: DMA addressing width in bits (32 or 64). Determines the
89+
+ * DMA mask capability of the controller hardware.
90+
*/
91+
struct mmp_pdma_ops {
92+
/* Hardware Register Operations */
93+
@@ -173,7 +173,7 @@ struct mmp_pdma_ops {
94+
95+
/* Controller Configuration */
96+
u32 run_bits;
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- u64 dma_mask;
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+ u32 dma_width;
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};
100+
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struct mmp_pdma_device {
102+
@@ -1172,7 +1172,7 @@ static const struct mmp_pdma_ops marvell_pdma_v1_ops = {
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.get_desc_src_addr = get_desc_src_addr_32,
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.get_desc_dst_addr = get_desc_dst_addr_32,
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.run_bits = (DCSR_RUN),
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- .dma_mask = 0, /* let OF/platform set DMA mask */
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+ .dma_width = 32,
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};
109+
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static const struct mmp_pdma_ops spacemit_k1_pdma_ops = {
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@@ -1185,7 +1185,7 @@ static const struct mmp_pdma_ops spacemit_k1_pdma_ops = {
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.get_desc_src_addr = get_desc_src_addr_64,
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.get_desc_dst_addr = get_desc_dst_addr_64,
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.run_bits = (DCSR_RUN | DCSR_LPAEEN),
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- .dma_mask = DMA_BIT_MASK(64), /* force 64-bit DMA addr capability */
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+ .dma_width = 64,
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};
118+
119+
static const struct of_device_id mmp_pdma_dt_ids[] = {
120+
@@ -1314,13 +1314,9 @@ static int mmp_pdma_probe(struct platform_device *op)
121+
pdev->device.directions = BIT(DMA_MEM_TO_DEV) | BIT(DMA_DEV_TO_MEM);
122+
pdev->device.residue_granularity = DMA_RESIDUE_GRANULARITY_DESCRIPTOR;
123+
124+
- /* Set DMA mask based on ops->dma_mask, or OF/platform */
125+
- if (pdev->ops->dma_mask)
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- dma_set_mask(pdev->dev, pdev->ops->dma_mask);
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- else if (pdev->dev->coherent_dma_mask)
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- dma_set_mask(pdev->dev, pdev->dev->coherent_dma_mask);
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- else
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- dma_set_mask(pdev->dev, DMA_BIT_MASK(64));
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+ /* Set DMA mask based on controller hardware capabilities */
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+ dma_set_mask_and_coherent(pdev->dev,
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+ DMA_BIT_MASK(pdev->ops->dma_width));
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ret = dma_async_device_register(&pdev->device);
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if (ret) {
137+
138+
---
139+
base-commit: cc0bacac6de7763a038550cf43cb94634d8be9cd
140+
change-id: 20250904-mmp-pdma-simplify-dma-addressing-f6aef03e07c3
141+
142+
Best regards,
143+
--
144+
Guodong Xu <[email protected]>
145+

‎patches/tip/series‎

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20250918_guodong_dmaengine_mmp_pdma_fix_dma_mask_handling.patch

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