mmc: sdhci-pci-gli: GL9767: Fix low power mode on the set clock function

On sdhci_gl9767_set_clock(), the vendor header space(VHS) is read-only
after calling gl9767_disable_ssc_pll() and gl9767_set_ssc_pll_205mhz().
So the low power negotiation mode cannot be enabled again.
Introduce gl9767_set_low_power_negotiation() function to fix it.

The explanation process is as below.

static void sdhci_gl9767_set_clock()
{
	...
        gl9767_vhs_write();
        ...
	value |= PCIE_GLI_9767_CFG_LOW_PWR_OFF;
        pci_write_config_dword(pdev, PCIE_GLI_9767_CFG, value); <--- (a)

        gl9767_disable_ssc_pll(); <--- (b)
        sdhci_writew(host, 0, SDHCI_CLOCK_CONTROL);

        if (clock == 0)
                return;  <-- (I)

	...
        if (clock == 200000000 && ios->timing == MMC_TIMING_UHS_SDR104) {
		...
                gl9767_set_ssc_pll_205mhz(); <--- (c)
        }
	...
	value &= ~PCIE_GLI_9767_CFG_LOW_PWR_OFF;
        pci_write_config_dword(pdev, PCIE_GLI_9767_CFG, value); <-- (II)
        gl9767_vhs_read();
}

(a) disable low power negotiation mode. When return on (I), the low power
mode is disabled.  After (b) and (c), VHS is read-only, the low power mode
cannot be enabled on (II).

Reported-by: Georg Gottleuber <[email protected]>
Fixes: d275435 ("mmc: sdhci-pci-gli: Set SDR104's clock to 205MHz and enable SSC for GL9767")
Signed-off-by: Ben Chuang <[email protected]>
Tested-by: Georg Gottleuber <[email protected]>
Cc: [email protected]
Message-ID: <[email protected]>
Signed-off-by: Ulf Hansson <[email protected]>

Author: benchuanggli

drivers/mmc/host/sdhci-pci-gli.c

@@ -892,28 +892,40 @@ static void gl9767_disable_ssc_pll(struct pci_dev *pdev)
 	gl9767_vhs_read(pdev);
 }
 
+static void gl9767_set_low_power_negotiation(struct pci_dev *pdev, bool enable)
+{
+	u32 value;
+
+	gl9767_vhs_write(pdev);
+
+	pci_read_config_dword(pdev, PCIE_GLI_9767_CFG, &value);
+	if (enable)
+		value &= ~PCIE_GLI_9767_CFG_LOW_PWR_OFF;
+	else
+		value |= PCIE_GLI_9767_CFG_LOW_PWR_OFF;
+	pci_write_config_dword(pdev, PCIE_GLI_9767_CFG, value);
+
+	gl9767_vhs_read(pdev);
+}
+
 static void sdhci_gl9767_set_clock(struct sdhci_host *host, unsigned int clock)
 {
 	struct sdhci_pci_slot *slot = sdhci_priv(host);
 	struct mmc_ios *ios = &host->mmc->ios;
 	struct pci_dev *pdev;
-	u32 value;
 	u16 clk;
 
 	pdev = slot->chip->pdev;
 	host->mmc->actual_clock = 0;
 
-	gl9767_vhs_write(pdev);
-
-	pci_read_config_dword(pdev, PCIE_GLI_9767_CFG, &value);
-	value |= PCIE_GLI_9767_CFG_LOW_PWR_OFF;
-	pci_write_config_dword(pdev, PCIE_GLI_9767_CFG, value);
-
+	gl9767_set_low_power_negotiation(pdev, false);
 	gl9767_disable_ssc_pll(pdev);
 	sdhci_writew(host, 0, SDHCI_CLOCK_CONTROL);
 
-	if (clock == 0)
+	if (clock == 0) {
+		gl9767_set_low_power_negotiation(pdev, true);
 		return;
+	}
 
 	clk = sdhci_calc_clk(host, clock, &host->mmc->actual_clock);
 	if (clock == 200000000 && ios->timing == MMC_TIMING_UHS_SDR104) {
@@ -922,12 +934,7 @@ static void sdhci_gl9767_set_clock(struct sdhci_host *host, unsigned int clock)
 	}
 
 	sdhci_enable_clk(host, clk);
-
-	pci_read_config_dword(pdev, PCIE_GLI_9767_CFG, &value);
-	value &= ~PCIE_GLI_9767_CFG_LOW_PWR_OFF;
-	pci_write_config_dword(pdev, PCIE_GLI_9767_CFG, value);
-
-	gl9767_vhs_read(pdev);
+	gl9767_set_low_power_negotiation(pdev, true);
 }
 
 static void gli_set_9767(struct sdhci_host *host)