drm/msm/dsi: fix error checks and return values for DSI xmit functions

[Marijn Suijten]

Hi Dmitry,

On 2022-04-02 02:11:04, Dmitry Baryshkov wrote:
> As noticed by Dan ([1] an the followup thread) there are multiple issues
> with the return values for MSM DSI command transmission callback. In
> the error case it can easily return a positive value when it should
> have returned a proper error code.
> 
> This commits attempts to fix these issues both in TX and in RX paths.
> 
> [1]: https://lore.kernel.org/linux-arm-msm/20211001123617.GH2283@kili/
> 
> Fixes: a689554ba6ed ("drm/msm: Initial add DSI connector support")
> Reported-by: Dan Carpenter <dan.carpenter at oracle.com>
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>
> Reviewed-by: Abhinav Kumar <quic_abhinavk at quicinc.com>

Thank you for your patience waiting for the requested tests; this patch
seems to have no adverse effect on our cmdmode panels.

Tested-by: Marijn Suijten <marijn.suijten at somainline.org>

On the following devices:
- Sony Xperia X (Loire Suzu, MSM8976), on Linux 5.17;
- Sony Xperia 10 II (Seine PDX201, SM6125), on -next 20220318;
- Sony Xperia XA2 Ultra (Nile Discovery, SDM630), on Linux 5.16.

Apologies for the older kernel versions, that's what happens when having
too many patches to dig through and too little hobby time to send them.
Let me know if there's a patch dependency that you like to be included.

- Marijn

> ---
>  drivers/gpu/drm/msm/dsi/dsi_host.c | 21 ++++++++++++++-------
>  1 file changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index d51e70fab93d..8925f60fd9ec 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -1341,10 +1341,10 @@ static int dsi_cmds2buf_tx(struct msm_dsi_host *msm_host,
>  			dsi_get_bpp(msm_host->format) / 8;
>  
>  	len = dsi_cmd_dma_add(msm_host, msg);
> -	if (!len) {
> +	if (len < 0) {
>  		pr_err("%s: failed to add cmd type = 0x%x\n",
>  			__func__,  msg->type);
> -		return -EINVAL;
> +		return len;
>  	}
>  
>  	/* for video mode, do not send cmds more than
> @@ -1363,10 +1363,14 @@ static int dsi_cmds2buf_tx(struct msm_dsi_host *msm_host,
>  	}
>  
>  	ret = dsi_cmd_dma_tx(msm_host, len);
> -	if (ret < len) {
> -		pr_err("%s: cmd dma tx failed, type=0x%x, data0=0x%x, len=%d\n",
> -			__func__, msg->type, (*(u8 *)(msg->tx_buf)), len);
> -		return -ECOMM;
> +	if (ret < 0) {
> +		pr_err("%s: cmd dma tx failed, type=0x%x, data0=0x%x, len=%d, ret=%d\n",
> +			__func__, msg->type, (*(u8 *)(msg->tx_buf)), len, ret);
> +		return ret;
> +	} else if (ret < len) {
> +		pr_err("%s: cmd dma tx failed, type=0x%x, data0=0x%x, ret=%d len=%d\n",
> +			__func__, msg->type, (*(u8 *)(msg->tx_buf)), ret, len);
> +		return -EIO;
>  	}
>  
>  	return len;
> @@ -2092,9 +2096,12 @@ int msm_dsi_host_cmd_rx(struct mipi_dsi_host *host,
>  		}
>  
>  		ret = dsi_cmds2buf_tx(msm_host, msg);
> -		if (ret < msg->tx_len) {
> +		if (ret < 0) {
>  			pr_err("%s: Read cmd Tx failed, %d\n", __func__, ret);
>  			return ret;
> +		} else if (ret < msg->tx_len) {
> +			pr_err("%s: Read cmd Tx failed, too short: %d\n", __func__, ret);
> +			return -ECOMM;
>  		}
>  
>  		/*