Hi Hans.
On Fri, Jul 8, 2022 at 9:28 PM Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
> On 7/8/22 20:21, Geert Uytterhoeven wrote:
> > If no mode name part was specified, mode_end is zero, and the "ret ==
> > mode_end" check does the wrong thing.
> >
> > Fix this by checking for a non-zero return value instead.
>
> Which is wrong to do, since now if you have e.g. a mode list
> with:
>
> "dblntsc",
> "dblntsc-ff"
>
> in there and the cmdline contains "dblntsc-ff" then you
> will already stop with a (wrong!) match at "dblntsc".
It indeed behaves that way, and did so before, as str_has_prefix()
checks for a matching prefix, and thus may never get to the full
match. However, can we change that to an exact match, without
introducing regressions?
This can be avoided by reverse-sorting the modelist (or iterating
backwards through a sorted modelist), though.
> > While at it, skip all named mode handling when mode_end is zero, as it
> > is futile.
>
> AFAICT, this is actually what needs to be done to fix this, while keeping
> the ret == mode_end check.
"ret == mode_end" or "ret" doesn't matter (except for the special
case of mode_end is zero), as str_has_prefix() returns either zero or
the length of the prefix. Hence it never returns a non-zero value
smaller than the length of the prefix.
> > Fixes: 7b1cce760afe38b4 ("drm/modes: parse_cmdline: Allow specifying stand-alone options")
> > Signed-off-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> > ---
> > drivers/gpu/drm/drm_modes.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
> > index 14b746f7ba975954..30a7be97707bfb16 100644
> > --- a/drivers/gpu/drm/drm_modes.c
> > +++ b/drivers/gpu/drm/drm_modes.c
> > @@ -1823,9 +1823,9 @@ bool drm_mode_parse_command_line_for_connector(const char *mode_option,
> > }
> >
> > /* First check for a named mode */
> > - for (i = 0; i < ARRAY_SIZE(drm_named_modes_whitelist); i++) {
> > + for (i = 0; mode_end && i < ARRAY_SIZE(drm_named_modes_whitelist); i++) {
> > ret = str_has_prefix(name, drm_named_modes_whitelist[i]);
> > - if (ret == mode_end) {
> > + if (ret) {
> > if (refresh_ptr)
> > return false; /* named + refresh is invalid */
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
