[PATCH v1] drm/bridge: tc358768: Fix DSI command tx

[Neil Armstrong]

On 26/09/2024 16:12, Francesco Dolcini wrote:
> From: Francesco Dolcini <francesco.dolcini at toradex.com>
> 
> Wait for the command transmission to be completed in the DSI transfer
> function polling for the dc_start bit to go back to idle state after the
> transmission is started.
> 
> This is documented in the datasheet and failures to do so lead to
> commands corruption.
> 
> Fixes: ff1ca6397b1d ("drm/bridge: Add tc358768 driver")
> Cc: stable at vger.kernel.org
> Signed-off-by: Francesco Dolcini <francesco.dolcini at toradex.com>
> ---
>   drivers/gpu/drm/bridge/tc358768.c | 21 +++++++++++++++++++--
>   1 file changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/tc358768.c b/drivers/gpu/drm/bridge/tc358768.c
> index 0e8813278a2f..bb1750a3dab0 100644
> --- a/drivers/gpu/drm/bridge/tc358768.c
> +++ b/drivers/gpu/drm/bridge/tc358768.c
> @@ -125,6 +125,9 @@
>   #define TC358768_DSI_CONFW_MODE_CLR	(6 << 29)
>   #define TC358768_DSI_CONFW_ADDR_DSI_CONTROL	(0x3 << 24)
>   
> +/* TC358768_DSICMD_TX (0x0600) register */
> +#define TC358768_DSI_CMDTX_DC_START	BIT(0)
> +
>   static const char * const tc358768_supplies[] = {
>   	"vddc", "vddmipi", "vddio"
>   };
> @@ -229,6 +232,21 @@ static void tc358768_update_bits(struct tc358768_priv *priv, u32 reg, u32 mask,
>   		tc358768_write(priv, reg, tmp);
>   }
>   
> +static void tc358768_dsicmd_tx(struct tc358768_priv *priv)
> +{
> +	u32 val;
> +
> +	/* start transfer */
> +	tc358768_write(priv, TC358768_DSICMD_TX, TC358768_DSI_CMDTX_DC_START);
> +	if (priv->error)
> +		return;
> +
> +	/* wait transfer completion */
> +	priv->error = regmap_read_poll_timeout(priv->regmap, TC358768_DSICMD_TX, val,
> +					       (val & TC358768_DSI_CMDTX_DC_START) == 0,
> +					       100, 100000);
> +}
> +
>   static int tc358768_sw_reset(struct tc358768_priv *priv)
>   {
>   	/* Assert Reset */
> @@ -516,8 +534,7 @@ static ssize_t tc358768_dsi_host_transfer(struct mipi_dsi_host *host,
>   		}
>   	}
>   
> -	/* start transfer */
> -	tc358768_write(priv, TC358768_DSICMD_TX, 1);
> +	tc358768_dsicmd_tx(priv);
>   
>   	ret = tc358768_clear_error(priv);
>   	if (ret)

Look good, I'll leave it here a few days if someone has comments

Reviewed-by: Neil Armstrong <neil.armstrong at linaro.org>