[PATCH v3] drm/mcde: Fix DSI transfers

[Stephan Gerhold]

On Tue, Sep 03, 2019 at 10:11:29AM +0200, Linus Walleij wrote:
> There were bugs in the DSI transfer (read and write) function
> as it was only tested with displays ever needing a single byte
> to be written. Fixed it up and tested so we can now write
> messages of up to 16 bytes and read up to 4 bytes from the
> display.
> 
> Tested with a Sony ACX424AKP display: this display now self-
> identifies and can control backlight in command mode.
> 
> Reported-by: kbuild test robot <lkp at intel.com>
> Fixes: 5fc537bfd000 ("drm/mcde: Add new driver for ST-Ericsson MCDE")
> Reviewed-by: Stephan Gerhold <stephan at gerhold.net>
> Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
> ---
> ChangeLog v2->v3:
> - Fix an error message to indicate reading error rather than
>   writing error.
> - Use the local variable for underflow print.
> - Collected Stephan's reviewed-by.
> ChangeLog v1->v2:
> - Fix a print modifier for dev_err() found by the build robot.
> ---
>  drivers/gpu/drm/mcde/mcde_dsi.c | 70 ++++++++++++++++++++++-----------
>  1 file changed, 47 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mcde/mcde_dsi.c b/drivers/gpu/drm/mcde/mcde_dsi.c
> index 07f7090d08b3..cd261c266f35 100644
> --- a/drivers/gpu/drm/mcde/mcde_dsi.c
> +++ b/drivers/gpu/drm/mcde/mcde_dsi.c
> @@ -178,22 +178,26 @@ static ssize_t mcde_dsi_host_transfer(struct mipi_dsi_host *host,
>  	const u32 loop_delay_us = 10; /* us */
>  	const u8 *tx = msg->tx_buf;
>  	u32 loop_counter;
> -	size_t txlen;
> +	size_t txlen = msg->tx_len;
> +	size_t rxlen = msg->rx_len;
>  	u32 val;
>  	int ret;
>  	int i;
>  
> -	txlen = msg->tx_len;
> -	if (txlen > 12) {
> +	if (txlen > 16) {
>  		dev_err(d->dev,
> -			"dunno how to write more than 12 bytes yet\n");
> +			"dunno how to write more than 16 bytes yet\n");
> +		return -EIO;
> +	}
> +	if (rxlen > 4) {
> +		dev_err(d->dev,
> +			"dunno how to read more than 4 bytes yet\n");
>  		return -EIO;
>  	}
>  
>  	dev_dbg(d->dev,
> -		"message to channel %d, %zd bytes",
> -		msg->channel,
> -		txlen);
> +		"message to channel %d, write %zd bytes read %zd bytes\n",
> +		msg->channel, txlen, rxlen);
>  
>  	/* Command "nature" */
>  	if (MCDE_DSI_HOST_IS_READ(msg->type))
> @@ -210,9 +214,7 @@ static ssize_t mcde_dsi_host_transfer(struct mipi_dsi_host *host,
>  	if (mipi_dsi_packet_format_is_long(msg->type))
>  		val |= DSI_DIRECT_CMD_MAIN_SETTINGS_CMD_LONGNOTSHORT;
>  	val |= 0 << DSI_DIRECT_CMD_MAIN_SETTINGS_CMD_ID_SHIFT;
> -	/* Add one to the length for the MIPI DCS command */
> -	val |= txlen
> -		<< DSI_DIRECT_CMD_MAIN_SETTINGS_CMD_SIZE_SHIFT;
> +	val |= txlen << DSI_DIRECT_CMD_MAIN_SETTINGS_CMD_SIZE_SHIFT;
>  	val |= DSI_DIRECT_CMD_MAIN_SETTINGS_CMD_LP_EN;
>  	val |= msg->type << DSI_DIRECT_CMD_MAIN_SETTINGS_CMD_HEAD_SHIFT;
>  	writel(val, d->regs + DSI_DIRECT_CMD_MAIN_SETTINGS);
> @@ -249,17 +251,36 @@ static ssize_t mcde_dsi_host_transfer(struct mipi_dsi_host *host,
>  	writel(1, d->regs + DSI_DIRECT_CMD_SEND);
>  
>  	loop_counter = 1000 * 1000 / loop_delay_us;
> -	while (!(readl(d->regs + DSI_DIRECT_CMD_STS) &
> -		 DSI_DIRECT_CMD_STS_WRITE_COMPLETED)
> -	       && --loop_counter)
> -		usleep_range(loop_delay_us, (loop_delay_us * 3) / 2);
> -
> -	if (!loop_counter) {
> -		dev_err(d->dev, "DSI write timeout!\n");
> -		return -ETIME;
> +	if (MCDE_DSI_HOST_IS_READ(msg->type)) {
> +		/* Read command */
> +		while (!(readl(d->regs + DSI_DIRECT_CMD_STS) &
> +			 (DSI_DIRECT_CMD_STS_READ_COMPLETED |
> +			  DSI_DIRECT_CMD_STS_READ_COMPLETED_WITH_ERR))
> +		       && --loop_counter)
> +			usleep_range(loop_delay_us, (loop_delay_us * 3) / 2);
> +		if (!loop_counter) {
> +			dev_err(d->dev, "DSI write timeout!\n");

It looks like you changed the wrong message.
This one is the "read timeout",

> +			return -ETIME;
> +		}
> +	} else {
> +		/* Writing only */
> +		while (!(readl(d->regs + DSI_DIRECT_CMD_STS) &
> +			 DSI_DIRECT_CMD_STS_WRITE_COMPLETED)
> +		       && --loop_counter)
> +			usleep_range(loop_delay_us, (loop_delay_us * 3) / 2);
> +
> +		if (!loop_counter) {
> +			dev_err(d->dev, "DSI read timeout!\n");

and this one the "write timeout".