On Tue, May 05, 2020 at 05:03:27PM +0100, Emil Velikov wrote:
> 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.nik...@intel.com>
> Cc: Thierry Reding <tred...@nvidia.com>
> Signed-off-by: Emil Velikov <emil.veli...@collabora.com>
Applied to drm-misc-next. Sorry for taking so long.
Sam
> ---
> drivers/gpu/drm/drm_mipi_dsi.c | 20 ++++++++++----------
> 1 file changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
> index 55531895dde6..b96d5b4629d7 100644
> --- a/drivers/gpu/drm/drm_mipi_dsi.c
> +++ b/drivers/gpu/drm/drm_mipi_dsi.c
> @@ -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;
> -
> + size = 1 + len;
> + if (len > ARRAY_SIZE(stack_tx) - 1) {
> tx = kmalloc(size, GFP_KERNEL);
> if (!tx)
> return -ENOMEM;
> -
> - /* concatenate the DCS command byte and the payload */
> - tx[0] = cmd;
> - memcpy(&tx[1], data, len);
> } else {
> - tx = &cmd;
> - size = 1;
> + tx = stack_tx;
> }
>
> + /* concatenate the DCS command byte and the payload */
> + tx[0] = cmd;
> + if (data)
> + memcpy(&tx[1], data, len);
> +
> err = mipi_dsi_dcs_write_buffer(dsi, tx, size);
>
> - if (len > 0)
> + if (tx != stack_tx)
> kfree(tx);
>
> return err;
> --
> 2.25.1
>
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