[PATCH 1/3] drm/dsi: use stack buffer in mipi_dsi_dcs_write()

[Thierry Reding]

On Thu, May 28, 2020 at 05:47:41PM +0100, Emil Velikov wrote:
> On Tue, 5 May 2020 at 17:05, Emil Velikov <emil.l.velikov at gmail.com> 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.nikula at intel.com>
> > Cc: Thierry Reding <treding at nvidia.com>
> > Signed-off-by: Emil Velikov <emil.velikov at collabora.com>
> > ---
> >  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;
> > --
> 
> Thierry, others - humble ping.
> Can you check through the series?

I don't see patch 2 of this series anywhere? Did it fall victim to some
filter?

Thierry
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