Re: [PATCH v2 1/2] drm/bridge/synopsys: dsi: use common mipi_dsi_create_packet()

[Philippe CORNU]

Hi Brian & All *DSI DRM experts*,

1) Re-reading this patch, I realize that the returned value of 
dw_mipi_dsi_host_transfer() is not correct: we should return the number 
of transfered/received bytes...

so I think there are two solutions: fix this in this serie or add a TODO 
for later (both solutions are fine to me :-)


2) Digging more into the drm code, the function 
mipi_dsi_device_transfer() in drm_mipi_dsi.c is called in the same file 
by the 3 following functions: mipi_dsi_shutdown_peripheral(), 
mipi_dsi_turn_on_peripheral() & 
mipi_dsi_set_maximum_return_packet_size(). All these 3 functions are 
expecting "Return: 0 on success or a negative error code on failure." 
that is not in line with the transfer function.

So then, we can change the documentation in this file and have instead 
"* Return: The number of bytes transmitted on success or a negative 
error code on failure." as for mipi_dsi_generic_write()...
Or we can change the source code of these 3 functions to match with the 
documentation "Return: 0 on success...".

note: Hopefully, "users" of these 3 functions test the sign of the 
return value (or do not use it).

Does anyone have a preferred solutions?

Many thanks
Philippe :-)

On 01/09/2018 09:32 PM, Brian Norris wrote:
> This takes care of 2 TODOs in this driver, by using the common DSI
> packet-marshalling code instead of our custom short/long write code.
> This both saves us some duplicated code and gets us free support for
> command types that weren't already part of our switch block (e.g.,
> MIPI_DSI_GENERIC_LONG_WRITE).
> 
> The code logic stays mostly intact, except that it becomes unnecessary
> to split the short/long write functions, and we have to copy data a bit
> more.
> 
> Along the way, I noticed that loop bounds were a little odd:
> 
> 	while (DIV_ROUND_UP(len, pld_data_bytes))
> 
> This really was just supposed to be 'len != 0', so I made that more
> clear.
> 
> Tested on RK3399 with some pending refactoring patches by Nickey Yang,
> to make the Rockchip DSI driver wrap this common driver.
> 
> Signed-off-by: Brian Norris <briannorris@xxxxxxxxxxxx>
> Reviewed-by: Philippe Cornu <philippe.cornu@xxxxxx>
> Tested-by: Philippe Cornu <philippe.cornu@xxxxxx>
> ---
> v2:
>   * remove "dcs" naming, since these commands handle generic DSI too, not
>     just DCS (thanks Philippe)
>   * add Philippe's {Tested,Reviewed}-by
> ---
>   drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c | 78 ++++++---------------------
>   1 file changed, 16 insertions(+), 62 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> index d9cca4fd66ec..ed91e32ee43a 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> @@ -136,10 +136,6 @@
>   					 GEN_SW_0P_TX_LP)
>   
>   #define DSI_GEN_HDR			0x6c
> -/* TODO These 2 defines will be reworked thanks to mipi_dsi_create_packet() */
> -#define GEN_HDATA(data)			(((data) & 0xffff) << 8)
> -#define GEN_HTYPE(type)			(((type) & 0xff) << 0)
> -
>   #define DSI_GEN_PLD_DATA		0x70
>   
>   #define DSI_CMD_PKT_STATUS		0x74
> @@ -359,44 +355,15 @@ static int dw_mipi_dsi_gen_pkt_hdr_write(struct dw_mipi_dsi *dsi, u32 hdr_val)
>   	return 0;
>   }
>   
> -static int dw_mipi_dsi_dcs_short_write(struct dw_mipi_dsi *dsi,
> -				       const struct mipi_dsi_msg *msg)
> -{
> -	const u8 *tx_buf = msg->tx_buf;
> -	u16 data = 0;
> -	u32 val;
> -
> -	if (msg->tx_len > 0)
> -		data |= tx_buf[0];
> -	if (msg->tx_len > 1)
> -		data |= tx_buf[1] << 8;
> -
> -	if (msg->tx_len > 2) {
> -		dev_err(dsi->dev, "too long tx buf length %zu for short write\n",
> -			msg->tx_len);
> -		return -EINVAL;
> -	}
> -
> -	val = GEN_HDATA(data) | GEN_HTYPE(msg->type);
> -	return dw_mipi_dsi_gen_pkt_hdr_write(dsi, val);
> -}
> -
> -static int dw_mipi_dsi_dcs_long_write(struct dw_mipi_dsi *dsi,
> -				      const struct mipi_dsi_msg *msg)
> +static int dw_mipi_dsi_write(struct dw_mipi_dsi *dsi,
> +			     const struct mipi_dsi_packet *packet)
>   {
> -	const u8 *tx_buf = msg->tx_buf;
> -	int len = msg->tx_len, pld_data_bytes = sizeof(u32), ret;
> -	u32 hdr_val = GEN_HDATA(msg->tx_len) | GEN_HTYPE(msg->type);
> +	const u8 *tx_buf = packet->payload;
> +	int len = packet->payload_length, pld_data_bytes = sizeof(u32), ret;
>   	u32 remainder;
>   	u32 val;
>   
> -	if (msg->tx_len < 3) {
> -		dev_err(dsi->dev, "wrong tx buf length %zu for long write\n",
> -			msg->tx_len);
> -		return -EINVAL;
> -	}
> -
> -	while (DIV_ROUND_UP(len, pld_data_bytes)) {
> +	while (len) {
>   		if (len < pld_data_bytes) {
>   			remainder = 0;
>   			memcpy(&remainder, tx_buf, len);
> @@ -419,40 +386,27 @@ static int dw_mipi_dsi_dcs_long_write(struct dw_mipi_dsi *dsi,
>   		}
>   	}
>   
> -	return dw_mipi_dsi_gen_pkt_hdr_write(dsi, hdr_val);
> +	remainder = 0;
> +	memcpy(&remainder, packet->header, sizeof(packet->header));
> +	return dw_mipi_dsi_gen_pkt_hdr_write(dsi, remainder);
>   }
>   
>   static ssize_t dw_mipi_dsi_host_transfer(struct mipi_dsi_host *host,
>   					 const struct mipi_dsi_msg *msg)
>   {
>   	struct dw_mipi_dsi *dsi = host_to_dsi(host);
> +	struct mipi_dsi_packet packet;
>   	int ret;
>   
> -	/*
> -	 * TODO dw drv improvements
> -	 * use mipi_dsi_create_packet() instead of all following
> -	 * functions and code (no switch cases, no
> -	 * dw_mipi_dsi_dcs_short_write(), only the loop in long_write...)
> -	 * and use packet.header...
> -	 */
> -	dw_mipi_message_config(dsi, msg);
> -
> -	switch (msg->type) {
> -	case MIPI_DSI_DCS_SHORT_WRITE:
> -	case MIPI_DSI_DCS_SHORT_WRITE_PARAM:
> -	case MIPI_DSI_SET_MAXIMUM_RETURN_PACKET_SIZE:
> -		ret = dw_mipi_dsi_dcs_short_write(dsi, msg);
> -		break;
> -	case MIPI_DSI_DCS_LONG_WRITE:
> -		ret = dw_mipi_dsi_dcs_long_write(dsi, msg);
> -		break;
> -	default:
> -		dev_err(dsi->dev, "unsupported message type 0x%02x\n",
> -			msg->type);
> -		ret = -EINVAL;
> +	ret = mipi_dsi_create_packet(&packet, msg);
> +	if (ret) {
> +		dev_err(dsi->dev, "failed to create packet: %d\n", ret);
> +		return ret;
>   	}
>   
> -	return ret;
> +	dw_mipi_message_config(dsi, msg);
> +
> +	return dw_mipi_dsi_write(dsi, &packet);
>   }
>   
>   static const struct mipi_dsi_host_ops dw_mipi_dsi_host_ops = {
>