linux-kernel - Re: [PATCH v3 4/4] drm/stm: add an option to change FB bpp

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Message-ID: <CAOf5uwmpAZeO=w-+cQNfy4VHS80NK-_HpDv5koZfTB8cRHOECQ@mail.gmail.com>
Date:   Tue, 13 Jun 2023 16:52:16 +0200
From:   Michael Nazzareno Trimarchi <michael@...rulasolutions.com>
To:     Philippe CORNU <philippe.cornu@...s.st.com>
Cc:     Dario Binacchi <dario.binacchi@...rulasolutions.com>,
        linux-kernel@...r.kernel.org,
        Amarula patchwork <linux-amarula@...rulasolutions.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...il.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Raphael Gallais-Pou <raphael.gallais-pou@...s.st.com>,
        Yannick Fertre <yannick.fertre@...s.st.com>,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH v3 4/4] drm/stm: add an option to change FB bpp

Hi

On Tue, Jun 13, 2023 at 4:41 PM Philippe CORNU
<philippe.cornu@...s.st.com> wrote:
>
>
>
> On 6/9/23 08:20, Dario Binacchi wrote:
> > Boards that use the STM32F{4,7} series have limited amounts of RAM. The
> > added parameter allows users to size, within certain limits, the memory
> > footprint required by the framebuffer.
> >
> > Signed-off-by: Dario Binacchi <dario.binacchi@...rulasolutions.com>
> >
> > ---
> >
> > Changes in v3:
> > - drop [4/6] dt-bindings: display: simple: add Rocktech RK043FN48H
> >    Applied to https://anongit.freedesktop.org/git/drm/drm-misc.git (drm-misc-next):
> >    https://cgit.freedesktop.org/drm/drm-misc/commit/?id=c42a37a27c777d63961dd634a30f7c887949491a
> > - drop [5/6] drm/panel: simple: add support for Rocktech RK043FN48H panel
> >    Applied to https://anongit.freedesktop.org/git/drm/drm-misc.git (drm-misc-next)
> >    https://cgit.freedesktop.org/drm/drm-misc/commit/?id=13cdd12a9f934158f4ec817cf048fcb4384aa9dc
> >
> >   drivers/gpu/drm/stm/drv.c | 8 +++++++-
> >   1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/stm/drv.c b/drivers/gpu/drm/stm/drv.c
> > index 422220df7d8c..65be2b442a6a 100644
> > --- a/drivers/gpu/drm/stm/drv.c
> > +++ b/drivers/gpu/drm/stm/drv.c
> > @@ -30,6 +30,11 @@
> >   #define STM_MAX_FB_WIDTH    2048
> >   #define STM_MAX_FB_HEIGHT   2048 /* same as width to handle orientation */
> >
> > +static uint stm_bpp = 16;
> > +
> > +MODULE_PARM_DESC(bpp, "bits-per-pixel (default: 16)");
> > +module_param_named(bpp, stm_bpp, uint, 0644);
> > +
> >   static const struct drm_mode_config_funcs drv_mode_config_funcs = {
> >       .fb_create = drm_gem_fb_create,
> >       .atomic_check = drm_atomic_helper_check,
> > @@ -93,6 +98,7 @@ static int drv_load(struct drm_device *ddev)
> >       ddev->mode_config.min_height = 0;
> >       ddev->mode_config.max_width = STM_MAX_FB_WIDTH;
> >       ddev->mode_config.max_height = STM_MAX_FB_HEIGHT;
> > +     ddev->mode_config.preferred_depth = stm_bpp;
> >       ddev->mode_config.funcs = &drv_mode_config_funcs;
> >       ddev->mode_config.normalize_zpos = true;
> >
> > @@ -203,7 +209,7 @@ static int stm_drm_platform_probe(struct platform_device *pdev)
> >       if (ret)
> >               goto err_put;
> >
> > -     drm_fbdev_dma_setup(ddev, 16);
> > +     drm_fbdev_dma_setup(ddev, stm_bpp);
> >
> >       return 0;
> >
>
> Acked-by: Philippe Cornu <philippe.cornu@...s.st.com>
> Many thanks,
> Philippe :-)
>

According to the latest review on usb patchset: "Please do not add new
module parameters, this is not the 1990's anymore.
We have per-device settings everywhere, this makes that impossible.
Just use a DT value, if it is wrong, then fix the DT value!  No need to
have the kernel override it, that's not what DT files are for."

I think it makes more sense to have dts parameters. Should maybe apply here too

Michael