linux-kernel - Re: [PATCH V6 4/6] drm: bridge: samsung-dsim: Select GENERIC_PHY_MIPI

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Date:   Wed, 17 May 2023 06:14:23 -0500
From:   Adam Ford <aford173@...il.com>
To:     Jagan Teki <jagan@...rulasolutions.com>
Cc:     dri-devel@...ts.freedesktop.org, aford@...conembedded.com,
        Frieder Schrempf <frieder.schrempf@...tron.de>,
        Chen-Yu Tsai <wenst@...omium.org>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Inki Dae <inki.dae@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Marek Vasut <marex@...x.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V6 4/6] drm: bridge: samsung-dsim: Select GENERIC_PHY_MIPI_DPHY

On Wed, May 17, 2023 at 6:05 AM Jagan Teki <jagan@...rulasolutions.com> wrote:
>
> Hi Adam,
>
> On Tue, May 16, 2023 at 5:27 AM Adam Ford <aford173@...il.com> wrote:
> >
> > In order to support variable DPHY timings, it's necessary
> > to enable GENERIC_PHY_MIPI_DPHY so phy_mipi_dphy_get_default_config
> > can be used to determine the nominal values for a given resolution
> > and refresh rate.
> >
> > Signed-off-by: Adam Ford <aford173@...il.com>
> > Tested-by: Frieder Schrempf <frieder.schrempf@...tron.de>
> > Reviewed-by: Frieder Schrempf <frieder.schrempf@...tron.de>
> > Tested-by: Chen-Yu Tsai <wenst@...omium.org>
> > ---
> >  drivers/gpu/drm/bridge/Kconfig | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> > index f076a09afac0..82c68b042444 100644
> > --- a/drivers/gpu/drm/bridge/Kconfig
> > +++ b/drivers/gpu/drm/bridge/Kconfig
> > @@ -227,6 +227,7 @@ config DRM_SAMSUNG_DSIM
> >         select DRM_KMS_HELPER
> >         select DRM_MIPI_DSI
> >         select DRM_PANEL_BRIDGE
> > +       select GENERIC_PHY_MIPI_DPHY
>
> Is it really required? phy is optional as it is not required for
> imx8mm/n/p as of now. May be we can add it while supporting it.

This was added to the series because build errors were reported
without it due to the fact that I added calls to
phy_mipi_dphy_get_default_config_for_hsclk.
Selecting this config option guarantees
phy_mipi_dphy_get_default_config_for_hsclk will be built and removes
the build error for Exynos and some 32-bit builds.

phy_mipi_dphy_get_default_config_for_hsclk sets the DSI configurations
like lpx, hs_exit, clk_prepare, clk_zero, clk_trail, hs_prepare,
hs_zero and hs_trail and those need to be
dynamic in order to functional at various resolutions.  I did try
leaving the hard-coded values you used, and I wasn't successful in
getting much to sync.

adam

>
> Thanks,
> Jagan.