Date:   Wed, 6 Oct 2021 11:37:20 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Stephen Boyd <swboyd@...omium.org>,
        Abhinav Kumar <abhinavk@...eaurora.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        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 Wed 06 Oct 10:19 PDT 2021, Dmitry Baryshkov wrote:

> On 06/10/2021 20:07, Bjorn Andersson wrote:
> > On Tue 05 Oct 21:26 PDT 2021, Stephen Boyd 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.
> > > 
> > > Maybe
> > > 
> > > 	struct msm_dp_desc {
> > > 		phys_addr_t io_start;
> > > 		unsigned int id;
> > 
> > The INTF_<N> constants are a property of the DPU driver and not
> > available in the DP driver and the msm_dp struct is a property of the DP
> > driver and can't be dereferenced in the DPU driver.
> > 
> > The proposed way around this is that the descs array defines the order
> > in priv->dp[N] and this N is used as controller_id.
> > 
> > 
> > So the only thing that I don't find straight forward here is that the
> > eDP controller is considered just a DP controller, so you have to use
> > INTF_DP, <N> for that, and not just INTF_EDP, 0.
> 
> Would it be better if we change the DPU driver to handle INTF_EDP too?
> 

I looked at that a while back and given that we can't look inside any of
the DP structs the only sensible solution I could come up with was to
create another array in struct msm_drm_private with "edp controllers".

But that means everywhere we today poke at priv->dp we need to also poke
at priv->edp. And the only gain is that we can say that the eDP
controller is INTF_EDP. And if there's ever a controller that could do
both, then that breaks down anyways.

Regards,
Bjorn

> > 
> > > 	};
> > > 
> > > and then have msm_dp_desc::id equal INTF_<N> and then look through the
> > > intf from DPU here in the DP driver to find the id and type of connector
> > > that should be used by default? Still sort of fragile because the only
> > > connection is an unsigned int which isn't great, but at least it's
> > > explicit instead of implicit based on the array order.
> > 
> > No matter how I look at this, you need to put some number somewhere here
> > that will be used to match up the INTF with the right DSI/DP encoder.
> > 
> > Using the proposed number scheme follows the numbering of all the DP
> > controllers from the documentation.
> > 
> > Regards,
> > Bjorn
> > 
> 
> 
> -- 
> With best wishes
> Dmitry

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