Commit e192fba2 authored May 05, 2020 by Emil Velikov Committed by Sam Ravnborg Jun 29, 2020

drm/dsi: use stack buffer in mipi_dsi_dcs_write()



Currently the function heap allocates when we have any payload. Where in
many case the payload is 1 byte - ouch.

>From casual observation, vast majority of the payloads are smaller than
8 bytes - so use a stack array tx[8] to avoid the senseless kmalloc and
kfree dance.

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Thierry Reding <treding@nvidia.com>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200505160329.2976059-1-emil.l.velikov@gmail.com

parent 8767c3fc

drivers/gpu/drm/drm_mipi_dsi.c

+10 −10

Original line number	Diff line number	Diff line
		@@ -748,26 +748,26 @@ ssize_t mipi_dsi_dcs_write(struct mipi_dsi_device *dsi, u8 cmd,
		{
		ssize_t err;
		size_t size;
		u8 stack_tx[8];
		u8 *tx;

		if (len > 0) {
		size = 1 + len;

		if (len > ARRAY_SIZE(stack_tx) - 1) {
		tx = kmalloc(size, GFP_KERNEL);
		if (!tx)
		return -ENOMEM;
		} else {
		tx = stack_tx;
		}

		/* concatenate the DCS command byte and the payload */
		tx[0] = cmd;
		if (data)
		memcpy(&tx[1], data, len);
		} else {
		tx = &cmd;
		size = 1;
		}

		err = mipi_dsi_dcs_write_buffer(dsi, tx, size);

		if (len > 0)
		if (tx != stack_tx)
		kfree(tx);

		return err;