Re: [PATCH 03/15] drm/dsi: Add mipi_dsi_set_maximum_return_packet_size() helper

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

On 10/13/2014 12:16 PM, Thierry Reding wrote:
> From: YoungJun Cho <yj44.cho@samsung.com>
> 
> This function can be used to set the maximum return packet size for a
> MIPI DSI peripheral.
> 
> Signed-off-by: YoungJun Cho <yj44.cho@samsung.com>
> [treding: endianess, kerneldoc, return value]
> Signed-off-by: Thierry Reding <treding@nvidia.com>
> ---
>  drivers/gpu/drm/drm_mipi_dsi.c | 30 ++++++++++++++++++++++++++++++
>  include/drm/drm_mipi_dsi.h     |  2 ++
>  2 files changed, 32 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
> index 1702ffd07986..27fc6dac5e4a 100644
> --- a/drivers/gpu/drm/drm_mipi_dsi.c
> +++ b/drivers/gpu/drm/drm_mipi_dsi.c
> @@ -198,6 +198,36 @@ int mipi_dsi_detach(struct mipi_dsi_device *dsi)
>  }
>  EXPORT_SYMBOL(mipi_dsi_detach);
>  
> +/*
> + * mipi_dsi_set_maximum_return_packet_size() - specify the maximum size of the
> + *    the payload in a long packet transmitted from the peripheral back to the
> + *    host processor
> + * @dsi: DSI peripheral device
> + * @value: the maximum size of the payload
> + *
> + * Return: 0 on success or a negative error code on failure.
> + */
> +int mipi_dsi_set_maximum_return_packet_size(struct mipi_dsi_device *dsi,
> +					    u16 value)
> +{
> +	u8 tx[2] = { value & 0xff, value >> 8 };
> +	struct mipi_dsi_msg msg;
> +	ssize_t err;
> +
> +	memset(&msg, 0, sizeof(msg));
> +	msg.channel = dsi->channel;
> +	msg.type = MIPI_DSI_SET_MAXIMUM_RETURN_PACKET_SIZE;
> +	msg.tx_len = sizeof(tx);
> +	msg.tx_buf = tx;


An alternative (without tx variable) could be:

	__cpu_to_le16s(&value);
	msg.tx_len = sizeof(value);
	msg.tx_buf = &value;

But it is just pico-optimization.


> +
> +	err = dsi->host->ops->transfer(dsi->host, &msg);

I guess the sequence:
	if (dsi->mode_flags & MIPI_DSI_MODE_LPM)
		msg.flags = MIPI_DSI_MSG_USE_LPM;

should be before this callback.

The same should be in all other helpers calling ops->transfer,
so I guess it may be good to move it all to separate function, for
example sth like:
... dsi_transfer(dsi, msg)
{
	if (!ops || !ops->transfer)
		return -NOSYS;

	if (dsi->mode_flags & MIPI_DSI_MODE_LPM)
		msg.flags = MIPI_DSI_MSG_USE_LPM;


	return ops->transfer(dsi->host, msg);
}

Regards
Andrzej

> +	if (err < 0)
> +		return err;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(mipi_dsi_set_maximum_return_packet_size);
> +
>  /**
>   * mipi_dsi_dcs_write_buffer() - transmit a DCS command with payload
>   * @dsi: DSI peripheral device
> diff --git a/include/drm/drm_mipi_dsi.h b/include/drm/drm_mipi_dsi.h
> index 836cc2b677d0..ef50b5d0de57 100644
> --- a/include/drm/drm_mipi_dsi.h
> +++ b/include/drm/drm_mipi_dsi.h
> @@ -132,6 +132,8 @@ static inline struct mipi_dsi_device *to_mipi_dsi_device(struct device *dev)
>  
>  int mipi_dsi_attach(struct mipi_dsi_device *dsi);
>  int mipi_dsi_detach(struct mipi_dsi_device *dsi);
> +int mipi_dsi_set_maximum_return_packet_size(struct mipi_dsi_device *dsi,
> +					    u16 value);
>  ssize_t mipi_dsi_dcs_write_buffer(struct mipi_dsi_device *dsi,
>  				  const void *data, size_t len);
>  ssize_t mipi_dsi_dcs_write(struct mipi_dsi_device *dsi, u8 cmd,
>