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

On Mon, Oct 13, 2014 at 04:10:31PM +0200, Andrzej Hajda wrote:

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); }

Good idea. It'd be slightly better if we could check for valid ops earlier, but I don't think it's really worth it. I'll add a helper that performs these common checks and rebase the other patches on top of it.

Thierry