phy: rockchip: phy-rockchip-inno-csidphy: allow writes to grf register 0

The driver for the Rockchip MIPI CSI-2 DPHY uses GRF register offset
value 0 to sort out undefined registers. However, the RK3588 CSIDPHY GRF
this offset is perfectly fine (in fact, register 0 is the only one in
this register file).
Introduce a boolean variable to indicate valid registers and allow writes
to register 0.

Reviewed-by: Neil Armstrong <[email protected]>
Signed-off-by: Michael Riesch <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Vinod Koul <[email protected]>

Author: Michael Riesch

drivers/phy/rockchip/phy-rockchip-inno-csidphy.c

@@ -87,10 +87,11 @@ struct dphy_reg {
 	u32 offset;
 	u32 mask;
 	u32 shift;
+	u8 valid;
 };
 
 #define PHY_REG(_offset, _width, _shift) \
-	{ .offset = _offset, .mask = BIT(_width) - 1, .shift = _shift, }
+	{ .offset = _offset, .mask = BIT(_width) - 1, .shift = _shift, .valid = 1, }
 
 static const struct dphy_reg rk1808_grf_dphy_regs[] = {
 	[GRF_DPHY_CSIPHY_FORCERXMODE] = PHY_REG(RK1808_GRF_PD_VI_CON_OFFSET, 4, 0),
@@ -145,7 +146,7 @@ static inline void write_grf_reg(struct rockchip_inno_csidphy *priv,
 	const struct dphy_drv_data *drv_data = priv->drv_data;
 	const struct dphy_reg *reg = &drv_data->grf_regs[index];
 
-	if (reg->offset)
+	if (reg->valid)
 		regmap_write(priv->grf, reg->offset,
 			     HIWORD_UPDATE(value, reg->mask, reg->shift));
 }