[PATCH v2 2/2] drm/msm/dsi: implement opp table based check for dsi_mgr_bridge_mode_valid()

[Dmitry Baryshkov]

On 12/01/2023 00:52, Abhinav Kumar wrote:
> Currently there is no protection against a user trying to set
> an unsupported mode on DSI. Implement a check based on the opp
> table whether the byte clock for the mode can be supported by
> validating whether an opp table entry exists.
> 
> For devices which have not added opp table support yet, skip
> this check otherwise it will break bootup on those devices.
> 
> changes in v2:
> 	- drop dev_pm_opp_get_opp_table() usage
> 
> Closes: https://gitlab.freedesktop.org/drm/msm/-/issues/15
> Reported-by: Rob Clark <robdclark at gmail.com>
> Signed-off-by: Abhinav Kumar <quic_abhinavk at quicinc.com>
> ---
>   drivers/gpu/drm/msm/dsi/dsi_manager.c | 25 +++++++++++++++++++++++++
>   1 file changed, 25 insertions(+)
> 
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_manager.c b/drivers/gpu/drm/msm/dsi/dsi_manager.c
> index 3a1417397283..c4c24dabfd6f 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_manager.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_manager.c
> @@ -450,6 +450,31 @@ static enum drm_mode_status dsi_mgr_bridge_mode_valid(struct drm_bridge *bridge,
>   	int id = dsi_mgr_bridge_get_id(bridge);
>   	struct msm_dsi *msm_dsi = dsi_mgr_get_dsi(id);
>   	struct mipi_dsi_host *host = msm_dsi->host;
> +	struct platform_device *pdev = msm_dsi->pdev;
> +	struct dev_pm_opp *opp;
> +	unsigned long byte_clk_rate;
> +
> +	byte_clk_rate = dsi_byte_clk_get_rate(host, IS_BONDED_DSI(), mode);
> +
> +	/*
> +	 * If dev_pm_opp_find_freq_ceil() returns -EINVAL, its a bad
> +	 * pointer being passed, so treat as an error and return MODE_ERROR
> +	 *
> +	 * If dev_pm_opp_find_freq_ceil() returns -ERANGE, no clock
> +	 * was found matching the byte_clk, so return MODE_CLOCK_RANGE
> +	 *
> +	 * If dev_pm_opp_find_freq_ceil() returns -ENODEV, don't treat
> +	 * it as an error as it could mean opp table is not implemented
> +	 */

I'd say, too lengthy and verbose.

> +	opp = dev_pm_opp_find_freq_ceil(&pdev->dev, &byte_clk_rate);
> +	if (IS_ERR(opp)) {
> +		if (PTR_ERR(opp) == -EINVAL)
> +			return MODE_ERROR;
> +		else if (PTR_ERR(opp) == -ERANGE)
> +			return MODE_CLOCK_RANGE;

I think the logic should be quite opposite. Ignore -ENODEV, handle 
-ERANGE and return MODE_ERROR for all other errors. In your code you are 
ignoring not only -ENODEV, but all other possible errors which can be 
added in future.

> +	} else {
> +		dev_pm_opp_put(opp);
> +	}
>   
>   	return msm_dsi_host_check_dsc(host, mode);
>   }

-- 
With best wishes
Dmitry