Re: [PATCH v4 5/7] drm/msm/dp: Support up to 3 DP controllers

[Dmitry Baryshkov <dmitry.baryshkov@linaro.org>]

Hi,

On Wed, 6 Oct 2021 at 10:06, Stephen Boyd <swboyd@chromium.org> wrote:
>
> Quoting Dmitry Baryshkov (2021-10-05 23:10:22)
> > On Wed, 6 Oct 2021 at 07:26, Stephen Boyd <swboyd@chromium.org> wrote:
> > >
> > > Quoting Bjorn Andersson (2021-10-05 19:37:52)
> > > > On Tue 05 Oct 19:06 PDT 2021, Stephen Boyd wrote:
> > > >
> > > > > Quoting Bjorn Andersson (2021-10-05 18:43:16)
> > > > > > On Tue 05 Oct 17:43 PDT 2021, Stephen Boyd wrote:
> > > > > >
> > > > > > > Quoting Bjorn Andersson (2021-10-05 16:13:21)
> > > > > > > > diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> > > > > > > > index bdaf227f05dc..674cddfee5b0 100644
> > > > > > > > --- a/drivers/gpu/drm/msm/dp/dp_display.c
> > > > > > > > +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> > > > > > > > @@ -1233,7 +1239,7 @@ static int dp_display_probe(struct platform_device *pdev)
> > > > > > > >         if (!dp)
> > > > > > > >                 return -ENOMEM;
> > > > > > > >
> > > > > > > > -       desc = dp_display_get_desc(pdev);
> > > > > > > > +       desc = dp_display_get_desc(pdev, &dp->id);
> > > > > > >
> > > > > > > I'm sad that dp->id has to match the number in the SoC specific
> > > > > > > dpu_intf_cfg array in drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.c
> > > > > > > still. Is there any way we can avoid that? Also, notice how those arrays
> > > > > > > already have INTF_DP macros, which makes me think that it may be better
> > > > > > > to connect this to those arrays instead of making an msm_dp_desc
> > > > > > > structure and then make sure the 'type' member matches a connector
> > > > > > > type number. Otherwise this code is super fragile.
> > > > > > >
> > > > > >
> > > > > > I'm afraid I don't understand what you're proposing. Or which part you
> > > > > > consider fragile, the indices of the INTF_DP instances aren't going to
> > > > > > move around...
> > > > > >
> > > > > > I have N instances of the DP driver that I need to match to N entries
> > > > > > from the platform specific intf array, I need some stable reference
> > > > > > between them. When I started this journey I figured I could rely on the
> > > > > > of_graph between the DPU and the interface controllers, but the values
> > > > > > used there today are just bogus, so that was a no go.
> > > > > >
> > > > > > We can use whatever, as long as _dpu_kms_initialize_displayport() can
> > > > > > come up with an identifier to put in h_tile_instance[0] so that
> > > > > > dpu_encoder_setup_display() can find the relevant INTF.
> > > > > >
> > > > >
> > > > > To make it more concrete we can look at sc7180
> > > > >
> > > > > static const struct dpu_intf_cfg sc7180_intf[] = {
> > > > >         INTF_BLK("intf_0", INTF_0, 0x6A000, INTF_DP, 0, 24,
> > > > > INTF_SC7180_MASK, MDP_SSPP_TOP0_INTR, 24, 25),
> > > > >                                                      ^
> > > > >                                                      |
> > > > >
> > > > > intf0 is irrelevant. Also the address is irrelevant. But here we have a
> > > > > zero, the number after INTF_DP, and that is very relevant. That number
> > > > > needs to match the dp->id. Somewhere we have a match between
> > > > > controller_id and dp->id in the code.
> > > >
> > > > That number (the 0, not INTF_0) is what the code matches against dp->id
> > > > in _dpu_kms_initialize_displayport(), in order to figure out that this
> > > > is INTF_0 in dpu_encoder_setup_display().
> > > >
> > > > I.e. look at the sc8180x patch:
> > > >
> > > > INTF_BLK("intf_0", INTF_0, 0x6A000, INTF_DP, 0, 24, INTF_SC8180X_MASK, MDP_SSPP_TOP0_INTR, 24, 25),
> > > > INTF_BLK("intf_1", INTF_1, 0x6A800, INTF_DSI, 0, 24, INTF_SC8180X_MASK, MDP_SSPP_TOP0_INTR, 26, 27),
> > > > INTF_BLK("intf_2", INTF_2, 0x6B000, INTF_DSI, 1, 24, INTF_SC8180X_MASK, MDP_SSPP_TOP0_INTR, 28, 29),
> > > > /* INTF_3 is for MST, wired to INTF_DP 0 and 1, use dummy index until this is supported */
> > > > INTF_BLK("intf_3", INTF_3, 0x6B800, INTF_DP, 999, 24, INTF_SC8180X_MASK, MDP_SSPP_TOP0_INTR, 30, 31),
> > > > INTF_BLK("intf_4", INTF_4, 0x6C000, INTF_DP, 1, 24, INTF_SC8180X_MASK, MDP_SSPP_TOP0_INTR, 20, 21),
> > > > INTF_BLK("intf_5", INTF_5, 0x6C800, INTF_DP, 2, 24, INTF_SC8180X_MASK, MDP_SSPP_TOP0_INTR, 22, 23),
> > > >
> > > > Where the DP driver defines the 3 controllers with dp->id of 0, 1 and 2,
> > > > which the DPU code will match against to INTF_0, INTF_4 and INTF_5.
> > > >
> > >
> > > Yep. I'm saying that having to make that number in this intf array match
> > > the order of the register mapping descriptor array is fragile. Why can't
> > > we indicate the interface is DP or eDP with INTF_DP or INTF_EDP and then
> > > map from the descriptor array to this intf array somehow so that the
> > > order of the descriptor array doesn't matter? Then we don't have to put
> > > the connector type in the descriptor array, and we don't have to keep
> > > the order of the array a certain way to match this intf descriptor.
> >
> > The order of the descriptor array does not matter currently (or we do
> > not understand fully your concern).
> > The encoder is mapped to intf using type + controller_id (next field
> > after INTF_foo).
> > Also having the controller_id in the descs array allows us to simplify
> > DSI code (where DSI_0 is master and DSI_1 is slave, no matter which
> > INTF they are associated with).
>
> The order seems to matter for me. Otherwise I get various vblank
> timeouts and the eDP panel doesn't light up. I'm using the previous
> version of this patch series though so maybe something got fixed in the
> meantime. If I change the controller_id to match my new ordering of the
> descriptor array then it works again. So somehow controller_id needs to
> match dp->id?

Yes, controller_id should match. However the order of entries in the
array should not matter. If it does, it's clearly an issue somewhere.

>
> >
> > Last, but not least, maybe I'd point you to one of the proposed
> > cleanup patches:
> > https://lore.kernel.org/linux-arm-msm/20210515225757.1989955-5-dmitry.baryshkov@linaro.org/
> > It removes one extra level of indirection in interface association.
> >
>
> Thanks for the link.



-- 
With best wishes
Dmitry