Re: [PATCH] drm/mcde: Retry DSI read/write transactions

[Stephan Gerhold <stephan@gerhold.net>]

On Thu, Jul 30, 2020 at 10:13:06AM +0200, Linus Walleij wrote:
> The vendor driver makes a few retries on read DSI
> transactions, something that is needed especially in
> case of read (such as reading the panel MTP ID) while
> the panel is running in video mode. This happens on
> the Samsung s6e63m0 panel on the Golden device.
> 

So this fixes reads from the panel for samsung-golden?

> Retry reads and writes alike two times.
> 
> Cc: Stephan Gerhold <stephan@gerhold.net>
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> ---
>  drivers/gpu/drm/mcde/mcde_dsi.c | 21 +++++++++++++++++++--
>  1 file changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mcde/mcde_dsi.c b/drivers/gpu/drm/mcde/mcde_dsi.c
> index 337c4c5e3947..76fecd7ab658 100644
> --- a/drivers/gpu/drm/mcde/mcde_dsi.c
> +++ b/drivers/gpu/drm/mcde/mcde_dsi.c
> @@ -207,8 +207,8 @@ static int mcde_dsi_host_detach(struct mipi_dsi_host *host,
>  	 (type == MIPI_DSI_GENERIC_READ_REQUEST_2_PARAM) || \
>  	 (type == MIPI_DSI_DCS_READ))
>  
> -static ssize_t mcde_dsi_host_transfer(struct mipi_dsi_host *host,
> -				      const struct mipi_dsi_msg *msg)
> +static ssize_t mcde_dsi_host_transfer_commit(struct mipi_dsi_host *host,
> +					     const struct mipi_dsi_msg *msg)
>  {
>  	struct mcde_dsi *d = host_to_mcde_dsi(host);
>  	const u32 loop_delay_us = 10; /* us */
> @@ -353,6 +353,23 @@ static ssize_t mcde_dsi_host_transfer(struct mipi_dsi_host *host,
>  	return ret;
>  }
>  
> +static ssize_t mcde_dsi_host_transfer(struct mipi_dsi_host *host,
> +				      const struct mipi_dsi_msg *msg)
> +{
> +	struct mcde_dsi *d = host_to_mcde_dsi(host);
> +	int retries = 2;
> +	ssize_t ret;
> +
> +	while (retries--) {
> +		ret = mcde_dsi_host_transfer_commit(host, msg);
> +		if (ret >= 0)
> +			return ret;
> +	}

I wonder if it would be better to do this inside
mcde_dsi_host_transfer_commit() - it seems like the vendor driver only
retries triggering the command, i.e.

	writel(~0, d->regs + DSI_DIRECT_CMD_STS_CLR);
	writel(~0, d->regs + DSI_CMD_MODE_STS_CLR);
	/* Send command */
	writel(1, d->regs + DSI_DIRECT_CMD_SEND);

and does not write all the registers again.

> +
> +	dev_err(d->dev, "gave up transfer after retrying\n");
> +	return ret;
> +}
> +
>  static const struct mipi_dsi_host_ops mcde_dsi_host_ops = {
>  	.attach = mcde_dsi_host_attach,
>  	.detach = mcde_dsi_host_detach,
> -- 
> 2.26.2
> 
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