Re: [PATCH] omapfb: dss: Fix max fclk divider for omap36xx

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Jul 08, 2020 at 06:37:51PM -0500, Adam Ford wrote:
> On Mon, Jul 6, 2020 at 6:18 AM Adam Ford <aford173@gmail.com> wrote:
> >
> > On Mon, Jul 6, 2020 at 1:02 AM Tomi Valkeinen <tomi.valkeinen@ti.com> wrote:
> > >
> > > Hi,
> > >
> > > On 03/07/2020 22:36, Sam Ravnborg wrote:
> > > > Hi Tomi.
> > > >
> > > > On Fri, Jul 03, 2020 at 10:17:29AM +0300, Tomi Valkeinen wrote:
> > > >> On 30/06/2020 21:26, Adam Ford wrote:
> > > >>> The drm/omap driver was fixed to correct an issue where using a
> > > >>> divider of 32 breaks the DSS despite the TRM stating 32 is a valid
> > > >>> number.  Through experimentation, it appears that 31 works, and
> > > >>> it is consistent with the value used by the drm/omap driver.
> > > >>>
> > > >>> This patch fixes the divider for fbdev driver instead of the drm.
> > > >>>
> > > >>> Fixes: f76ee892a99e ("omapfb: copy omapdss & displays for omapfb")
> > > >>>
> > > >>> Cc: <stable@vger.kernel.org> #4.9+
> > > >>> Signed-off-by: Adam Ford <aford173@gmail.com>
> > > >>> ---
> > > >>> Linux 4.4 will need a similar patch, but it doesn't apply cleanly.
> > > >>>
> > > >>> The DRM version of this same fix is:
> > > >>> e2c4ed148cf3 ("drm/omap: fix max fclk divider for omap36xx")
> > > >>>
> > > >>>
> > > >>> diff --git a/drivers/video/fbdev/omap2/omapfb/dss/dss.c b/drivers/video/fbdev/omap2/omapfb/dss/dss.c
> > > >>> index 7252d22dd117..bfc5c4c5a26a 100644
> > > >>> --- a/drivers/video/fbdev/omap2/omapfb/dss/dss.c
> > > >>> +++ b/drivers/video/fbdev/omap2/omapfb/dss/dss.c
> > > >>> @@ -833,7 +833,7 @@ static const struct dss_features omap34xx_dss_feats = {
> > > >>>    };
> > > >>>    static const struct dss_features omap3630_dss_feats = {
> > > >>> -   .fck_div_max            =       32,
> > > >>> +   .fck_div_max            =       31,
> > > >>>     .dss_fck_multiplier     =       1,
> > > >>>     .parent_clk_name        =       "dpll4_ck",
> > > >>>     .dpi_select_source      =       &dss_dpi_select_source_omap2_omap3,
> > > >>>
> > > >>
> > > >> Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
> > > > Will you apply to drm-misc?
> > >
> > > This is for fbdev, so I presume Bartlomiej will pick this one.
> > >
> > > > Note  following output from "dim fixes":
> > > > $ dim fixes f76ee892a99e
> > > > Fixes: f76ee892a99e ("omapfb: copy omapdss & displays for omapfb")
> > > > Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
> > > > Cc: Dave Airlie <airlied@gmail.com>
> > > > Cc: Rob Clark <robdclark@gmail.com>
> > > > Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > > > Cc: Sam Ravnborg <sam@ravnborg.org>
> > > > Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
> > > > Cc: Jason Yan <yanaijie@huawei.com>
> > > > Cc: "Andrew F. Davis" <afd@ti.com>
> > > > Cc: YueHaibing <yuehaibing@huawei.com>
> > > > Cc: <stable@vger.kernel.org> # v4.5+
> > > >
> > > > Here it says the fix is valid from v4.5 onwards.
> > >
> > > Hmm... Adam, you marked the fix to apply to v4.9+, and then you said
> > > v4.4 needs a new patch (that's before the big copy/rename). Did you
> > > check the versions between 4.4 and 4.9? I would guess this one applies
> > > to v4.5+.
> >
> > I only tried 4.9 because it's listed as an LTS kernel.  The stuff
> > between 4.4 and 4.9 were EOL, so I didn't go back further.    The 4.5+
> > is probably more accurate.  I would like to do the same thing for the
> > 4.4 kernel, but I am not sure the proper way to do that.
> 
> What is the correct protocol for patching 4.4?  I'd like to do that,
> but the patch would be unique to the 4.4.  Should I just submit the
> patch directly to stable and cc Tomi?

Yes, and document the heck out of why this is a 4.4-only patch, and why
we can't take whatever happened in newer kernels instead.

thanks,

greg k-h