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

From: Dmitry Baryshkov
Date: Wed Oct 06 2021 - 13:19:44 EST

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?


};

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