[PATCH v2 1/2] drm/msm/dsi: Use "ref" fw clock instead of global name for VCO parent

[Stephen Boyd]

Quoting Marijn Suijten (2021-08-30 15:45:42)
> Hi Stephen,
> 
> On 2021-08-30 15:16:13, Stephen Boyd wrote:
> > Quoting Marijn Suijten (2021-08-30 11:24:44)
> > > All DSI PHY/PLL drivers were referencing their VCO parent clock by a
> > > global name, most of which don't exist or have been renamed.  These
> > > clock drivers seem to function fine without that except the 14nm driver
> > > for the sdm6xx [1].
> > > 
> > > At the same time all DTs provide a "ref" clock as per the requirements
> > > of dsi-phy-common.yaml, but the clock is never used.  This patchset puts
> > > that clock to use without relying on a global clock name, so that all
> > > dependencies are explicitly defined in DT (the firmware) in the end.
> > > 
> > > Note that msm8974 is the only board not providing this clock, and
> > > apq8064 was providing the wrong clock (19.2MHz cxo instead of 27MHz
> > > pxo).  Both have been been addressed in separate patches that are
> > > supposed to land well in advance of this patchset.
> > > 
> > > Furthermore not all board-DTs provided this clock initially but that
> > > deficiency has been addressed in followup patches (see the Fixes:
> > > below).  Those commits seem to assume that the clock was used, while
> > > nothing in history indicates that this "ref" clock was ever retrieved.
> > > 
> > > [1]: https://lore.kernel.org/linux-arm-msm/386db1a6-a1cd-3c7d-a88e-dc83f8a1be96@somainline.org/
> > > 
> > > Fixes: 79e51645a1dd ("arm64: dts: qcom: msm8916: Set 'xo_board' as ref clock of the DSI PHY")
> > > Fixes: 6969d1d9c615 ("ARM: dts: qcom-apq8064: Set 'cxo_board' as ref clock of the DSI PHY")
> > > Fixes: 0c0e72705a33 ("arm64: dts: sdm845: Set 'bi_tcxo' as ref clock of the DSI PHYs")
> > > Signed-off-by: Marijn Suijten <marijn.suijten at somainline.org>
> > > ---
> > >  drivers/gpu/drm/msm/dsi/phy/dsi_phy_10nm.c      | 4 +++-
> > >  drivers/gpu/drm/msm/dsi/phy/dsi_phy_14nm.c      | 4 +++-
> > >  drivers/gpu/drm/msm/dsi/phy/dsi_phy_28nm.c      | 4 +++-
> > >  drivers/gpu/drm/msm/dsi/phy/dsi_phy_28nm_8960.c | 4 +++-
> > >  drivers/gpu/drm/msm/dsi/phy/dsi_phy_7nm.c       | 4 +++-
> > >  5 files changed, 15 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/msm/dsi/phy/dsi_phy_10nm.c b/drivers/gpu/drm/msm/dsi/phy/dsi_phy_10nm.c
> > > index e46b10fc793a..3cbb1f1475e8 100644
> > > --- a/drivers/gpu/drm/msm/dsi/phy/dsi_phy_10nm.c
> > > +++ b/drivers/gpu/drm/msm/dsi/phy/dsi_phy_10nm.c
> > > @@ -562,7 +562,9 @@ static int pll_10nm_register(struct dsi_pll_10nm *pll_10nm, struct clk_hw **prov
> > >         char clk_name[32], parent[32], vco_name[32];
> > >         char parent2[32], parent3[32], parent4[32];
> > >         struct clk_init_data vco_init = {
> > > -               .parent_names = (const char *[]){ "xo" },
> > > +               .parent_data = &(const struct clk_parent_data) {
> > > +                       .fw_name = "ref",
> > 
> > Please also add .name as the old parent_names value so that newer
> > kernels can be used without having to use new DT.
> 
> We discussed that only msm8974 misses this "ref" clock at the time of
> writing.  Aforementioned Fixes: patches have all been merged about 3
> years ago, are those DTs still in use with a newer kernel?  I suppose
> this patch is only backported to kernels including those DT patches, is
> it reasonable to assume that at least that DT is in use there?

I have no idea.

> 
> Besides, not all clock trees provide this global "xo" or "bi_tcxo" clock
> in the first place.
> 

It doesn't hurt to also specify a .name to help migrate anything else
over. Unless you're confident it won't cause problems to rely on proper
DT being used?