linux-kernel - Re: [PATCH v2] drm/mediatek: allow commands to be sent during video mode

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Date:   Thu, 10 Feb 2022 17:36:14 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Julien STEPHAN <jstephan@...libre.com>, ck.hu@...iatek.com
Cc:     Mattijs Korpershoek <mkorpershoek@...libre.com>,
        Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "open list:DRM DRIVERS FOR MEDIATEK" 
        <dri-devel@...ts.freedesktop.org>,
        "moderated list:DRM DRIVERS FOR MEDIATEK" 
        <linux-mediatek@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] drm/mediatek: allow commands to be sent during video
 mode

Il 10/02/22 13:46, Julien STEPHAN ha scritto:
> Mipi dsi panel drivers can use mipi_dsi_dcs_{set,get}_display_brightness()
> to request backlight changes.
> 
> This can be done during panel initialization (dsi is in command mode)
> or afterwards (dsi is in Video Mode).
> 
> When the DSI is in Video Mode, all commands are rejected.
> 
> Detect current DSI mode in mtk_dsi_host_transfer() and switch modes
> temporarily to allow commands to be sent.
> 
> Signed-off-by: Julien STEPHAN <jstephan@...libre.com>
> Signed-off-by: Mattijs Korpershoek <mkorpershoek@...libre.com>
> Reviewed-by: Chun-Kuang Hu <chunkuang.hu@...nel.org>

Hello Julien,
thanks for the patch!

However, there's a severe issue to solve.

> ---
> Changes in v2:
>    - update commit message to be more descriptive
> 
>   drivers/gpu/drm/mediatek/mtk_dsi.c | 34 ++++++++++++++++++++++--------
>   1 file changed, 25 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c b/drivers/gpu/drm/mediatek/mtk_dsi.c
> index 5d90d2eb0019..7d66fdc7f81d 100644
> --- a/drivers/gpu/drm/mediatek/mtk_dsi.c
> +++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
> @@ -891,24 +891,34 @@ static ssize_t mtk_dsi_host_transfer(struct mipi_dsi_host *host,
>   	u8 read_data[16];
>   	void *src_addr;
>   	u8 irq_flag = CMD_DONE_INT_FLAG;
> -
> -	if (readl(dsi->regs + DSI_MODE_CTRL) & MODE) {
> -		DRM_ERROR("dsi engine is not command mode\n");
> -		return -EINVAL;
> +	u32 dsi_mode;
> +
> +	dsi_mode = readl(dsi->regs + DSI_MODE_CTRL);
> +	if (dsi_mode & MODE) {
> +		mtk_dsi_stop(dsi);
> +		if (mtk_dsi_switch_to_cmd_mode(dsi, VM_DONE_INT_FLAG, 500)) {
> +			recv_cnt = -EINVAL;

Variable recv_cnt is u32, hence unsigned... You cannot assign a negative error
number to that variable.

While at it, please add a `int ret` variable to increase readability of this
function after your additions... in which case, this would then be

		ret = mtk_dsi_switch_to_cmd_mode(dsi, VM_DONE_INT_FLAG, 500);
		if (ret)
			goto restore_dsi_mode;

...which also simplifies the flow, in my opinion (but that's personal preference).

> +			goto restore_dsi_mode;
> +		}
>   	}
>   
>   	if (MTK_DSI_HOST_IS_READ(msg->type))
>   		irq_flag |= LPRX_RD_RDY_INT_FLAG;
>   
> -	if (mtk_dsi_host_send_cmd(dsi, msg, irq_flag) < 0)
> -		return -ETIME;
> +	if (mtk_dsi_host_send_cmd(dsi, msg, irq_flag) < 0) {
> +		recv_cnt = -ETIME;

This can be improved: mtk_dsi_host_send_cmd() already returns either zero or
-ETIME if mtk_dsi_wait_for_irq_done() times out.

I would also suggest, at this point, to make function mtk_dsi_wait_for_irq_done()
directly return -ETIME, so that also mtk_dsi_switch_to_cmd_mode() and
mtk_dsi_host_send_cmd() are simplified.

Whether you want to improve this file, or want to avoid improving it right now,
this should anyway be like:

	ret = mtk_dsi_host_send_cmd(..blah)
	if (ret)
		goto restore_dsi_mode;

> +		goto restore_dsi_mode;
> +	}
>   
> -	if (!MTK_DSI_HOST_IS_READ(msg->type))
> -		return 0;
> +	if (!MTK_DSI_HOST_IS_READ(msg->type)) {
> +		recv_cnt = 0;
> +		goto restore_dsi_mode;
> +	}
>   
>   	if (!msg->rx_buf) {
>   		DRM_ERROR("dsi receive buffer size may be NULL\n");
> -		return -EINVAL;
> +		recv_cnt = -EINVAL;
> +		goto restore_dsi_mode;
>   	}
>   
>   	for (i = 0; i < 16; i++)
> @@ -933,6 +943,12 @@ static ssize_t mtk_dsi_host_transfer(struct mipi_dsi_host *host,
>   	DRM_INFO("dsi get %d byte data from the panel address(0x%x)\n",
>   		 recv_cnt, *((u8 *)(msg->tx_buf)));
>   
> +restore_dsi_mode:
> +	if (dsi_mode & MODE) {
> +		mtk_dsi_set_mode(dsi);
> +		mtk_dsi_start(dsi);
> +	}
> +
>   	return recv_cnt;

P.S.:   return ret < 0 ? ret : recv_cnt;

>   }
>   
> 

Thanks,
Angelo