Re: [PATCH v5 12/22] drm/connector: Add a function to lookup a TV mode by its name

Maxime Ripard
2022-10-19T08:49:55Z

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On Tue, Oct 18, 2022 at 02:29:00PM +0200, Noralf Trønnes wrote:
>
>
> Den 18.10.2022 11.33, skrev Maxime Ripard:
> > On Mon, Oct 17, 2022 at 12:44:45PM +0200, Noralf Trønnes wrote:
> >> Den 13.10.2022 15.18, skrev Maxime Ripard:
> >>> As part of the command line parsing rework coming in the next patches,
> >>> we'll need to lookup drm_connector_tv_mode values by their name, already
> >>> defined in drm_tv_mode_enum_list.
> >>>
> >>> In order to avoid any code duplication, let's do a function that will
> >>> perform a lookup of a TV mode name and return its value.
> >>>
> >>> Signed-off-by: Maxime Ripard <maxime@cerno.tech>
> >>> ---
> >>> drivers/gpu/drm/drm_connector.c | 24 ++++++++++++++++++++++++
> >>> include/drm/drm_connector.h | 2 ++
> >>> 2 files changed, 26 insertions(+)
> >>>
> >>> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> >>> index 820f4c730b38..30611c616435 100644
> >>> --- a/drivers/gpu/drm/drm_connector.c
> >>> +++ b/drivers/gpu/drm/drm_connector.c
> >>> @@ -991,6 +991,30 @@ static const struct drm_prop_enum_list drm_tv_mode_enum_list[] = {
> >>> };
> >>> DRM_ENUM_NAME_FN(drm_get_tv_mode_name, drm_tv_mode_enum_list)
> >>>
> >>> +/**
> >>> + * drm_get_tv_mode_from_name - Translates a TV mode name into its enum value
> >>> + * @name: TV Mode name we want to convert
> >>> + * @len: Length of @name
> >>> + *
> >>> + * Translates @name into an enum drm_connector_tv_mode.
> >>> + *
> >>> + * Returns: the enum value on success, a negative errno otherwise.
> >>> + */
> >>> +int drm_get_tv_mode_from_name(const char *name, size_t len)
> >>
> >> Do we really need to pass in length here? item->name has to always be
> >> NUL terminated otherwise things would break elsewhere, so it shouldn't
> >> be necessary AFAICS.
> >
> > The only user so far is the command-line parsing code, and we might very
> > well have an option after the tv_mode, something like
> > 720x480i,tv_mode=NTSC,rotate=180
> >
> > In this case, we won't get a NULL-terminated name.
>
> My point is that item->name will always be NUL terminated so strcmp()
> will never look past that.

Right, but we don't have the guarantee that strlen(item->name) <
strlen(name), and we could thus just access after the end of our name

Maxime

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