Re: [PATCH 3/4] drm/dsi: Make mipi_dsi_dcs_{read, write}() symmetrical

[Andrzej Hajda <a.hajda@samsung.com>]

On 07/22/2014 09:12 AM, Thierry Reding wrote:
> From: Thierry Reding <treding@nvidia.com>
>
> Currently the mipi_dsi_dcs_write() function requires the DCS command
> byte to be embedded within the write buffer whereas mipi_dsi_dcs_read()
> has a separate parameter. Make them more symmetrical by adding an extra
> command parameter to mipi_dsi_dcs_write().
>
> Also update the S6E8AA0 panel driver (the only user of this API) to
> adapt to this new API.

I do not agree with that. DCS read and write are not symmetrical by design:
- write just sends data,
- read sends data then reads response.

Forcing API to be symmetrical complicates the implementation without real gain.

Regards
Andrzej



>
> Signed-off-by: Thierry Reding <treding@nvidia.com>
> ---
>  drivers/gpu/drm/drm_mipi_dsi.c        | 45 ++++++++++++++++++++++++-----------
>  drivers/gpu/drm/panel/panel-s6e8aa0.c |  4 ++--
>  include/drm/drm_mipi_dsi.h            |  4 ++--
>  3 files changed, 35 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
> index 6aa6a9e95570..bbab06ef80c9 100644
> --- a/drivers/gpu/drm/drm_mipi_dsi.c
> +++ b/drivers/gpu/drm/drm_mipi_dsi.c
> @@ -201,29 +201,41 @@ EXPORT_SYMBOL(mipi_dsi_detach);
>  /**
>   * mipi_dsi_dcs_write - send DCS write command
>   * @dsi: DSI device
> - * @data: pointer to the command followed by parameters
> - * @len: length of @data
> + * @cmd: DCS command
> + * @data: pointer to the command payload
> + * @len: payload length
>   */
> -ssize_t mipi_dsi_dcs_write(struct mipi_dsi_device *dsi, const void *data,
> -			    size_t len)
> +ssize_t mipi_dsi_dcs_write(struct mipi_dsi_device *dsi, u8 cmd,
> +			   const void *data, size_t len)
>  {
>  	const struct mipi_dsi_host_ops *ops = dsi->host->ops;
> -	struct mipi_dsi_msg msg = {
> -		.channel = dsi->channel,
> -		.tx_buf = data,
> -		.tx_len = len
> -	};
> +	struct mipi_dsi_msg msg;
> +	ssize_t err;
> +	u8 *tx;
>  
>  	if (!ops || !ops->transfer)
>  		return -ENOSYS;
>  
> +	if (len > 0) {
> +		tx = kmalloc(1 + len, GFP_KERNEL);
> +		if (!tx)
> +			return -ENOMEM;
> +
> +		tx[0] = cmd;
> +		memcpy(tx + 1, data, len);
> +	} else {
> +		tx = &cmd;
> +	}
> +
> +	msg.channel = dsi->channel;
> +	msg.tx_len = 1 + len;
> +	msg.tx_buf = tx;
> +
>  	switch (len) {
>  	case 0:
> -		return -EINVAL;
> -	case 1:
>  		msg.type = MIPI_DSI_DCS_SHORT_WRITE;
>  		break;
> -	case 2:
> +	case 1:
>  		msg.type = MIPI_DSI_DCS_SHORT_WRITE_PARAM;
>  		break;
>  	default:
> @@ -231,14 +243,19 @@ ssize_t mipi_dsi_dcs_write(struct mipi_dsi_device *dsi, const void *data,
>  		break;
>  	}
>  
> -	return ops->transfer(dsi->host, &msg);
> +	err = ops->transfer(dsi->host, &msg);
> +
> +	if (len > 0)
> +		kfree(tx);
> +
> +	return err;
>  }
>  EXPORT_SYMBOL(mipi_dsi_dcs_write);
>  
>  /**
>   * mipi_dsi_dcs_read - send DCS read request command
>   * @dsi: DSI device
> - * @cmd: DCS read command
> + * @cmd: DCS command
>   * @data: pointer to read buffer
>   * @len: length of @data
>   *
> diff --git a/drivers/gpu/drm/panel/panel-s6e8aa0.c b/drivers/gpu/drm/panel/panel-s6e8aa0.c
> index 5502ef6bc074..d39bee36816c 100644
> --- a/drivers/gpu/drm/panel/panel-s6e8aa0.c
> +++ b/drivers/gpu/drm/panel/panel-s6e8aa0.c
> @@ -130,7 +130,7 @@ static int s6e8aa0_clear_error(struct s6e8aa0 *ctx)
>  	return ret;
>  }
>  
> -static void s6e8aa0_dcs_write(struct s6e8aa0 *ctx, const void *data, size_t len)
> +static void s6e8aa0_dcs_write(struct s6e8aa0 *ctx, const u8 *data, size_t len)
>  {
>  	struct mipi_dsi_device *dsi = to_mipi_dsi_device(ctx->dev);
>  	ssize_t ret;
> @@ -138,7 +138,7 @@ static void s6e8aa0_dcs_write(struct s6e8aa0 *ctx, const void *data, size_t len)
>  	if (ctx->error < 0)
>  		return;
>  
> -	ret = mipi_dsi_dcs_write(dsi, data, len);
> +	ret = mipi_dsi_dcs_write(dsi, data[0], data + 1, len - 1);
>  	if (ret < 0) {
>  		dev_err(ctx->dev, "error %zd writing dcs seq: %*ph\n", ret, len,
>  			data);
> diff --git a/include/drm/drm_mipi_dsi.h b/include/drm/drm_mipi_dsi.h
> index 7b5e1a9244e1..bea181121e8b 100644
> --- a/include/drm/drm_mipi_dsi.h
> +++ b/include/drm/drm_mipi_dsi.h
> @@ -127,8 +127,8 @@ struct mipi_dsi_device {
>  
>  int mipi_dsi_attach(struct mipi_dsi_device *dsi);
>  int mipi_dsi_detach(struct mipi_dsi_device *dsi);
> -ssize_t mipi_dsi_dcs_write(struct mipi_dsi_device *dsi, const void *data,
> -			    size_t len);
> +ssize_t mipi_dsi_dcs_write(struct mipi_dsi_device *dsi, u8 cmd,
> +			   const void *data, size_t len);
>  ssize_t mipi_dsi_dcs_read(struct mipi_dsi_device *dsi, u8 cmd, void *data,
>  			  size_t len);
>