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

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Message-ID: <YV0MAF/Y5BR1e6My@ripper>
Date:   Tue, 5 Oct 2021 19:37:52 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Abhinav Kumar <abhinavk@...eaurora.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Kalyan Thota <kalyan_t@...eaurora.org>,
        Kuogee Hsieh <khsieh@...eaurora.org>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 5/7] drm/msm/dp: Support up to 3 DP controllers

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.

Regards,
Bjorn