| Message ID | 64e2e9b14c26df28908789374253fd12072c26c2.1657301107.git.geert@linux-m68k.org |
|---|---|
| State | New |
| Headers | show |
| Series | drm/modes: Command line mode selection fixes and improvements | expand |
Hi Geert, 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". > 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. Regards, Hans > > Fixes: 7b1cce760afe38b4 ("drm/modes: parse_cmdline: Allow specifying stand-alone options") > Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org> > --- > 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 */ >
Hi Hans. On Fri, Jul 8, 2022 at 9:28 PM Hans de Goede <hdegoede@redhat.com> 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@linux-m68k.org> > > --- > > 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@linux-m68k.org 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
Hi Hans, On Fri, Jul 8, 2022 at 10:06 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > On Fri, Jul 8, 2022 at 9:28 PM Hans de Goede <hdegoede@redhat.com> 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. Ignore that. I finally saw what's really happening. And I do agree with your comment. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org 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
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 */
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. While at it, skip all named mode handling when mode_end is zero, as it is futile. Fixes: 7b1cce760afe38b4 ("drm/modes: parse_cmdline: Allow specifying stand-alone options") Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org> --- drivers/gpu/drm/drm_modes.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)