Re: [PATCH v8 7/8] drm/msm/dpu: add DSC 1.2 hw blocks for relevant chipsets

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On 5/15/2023 3:23 PM, Marijn Suijten wrote:
On 2023-05-15 15:03:46, Abhinav Kumar wrote:
On 5/15/2023 2:21 PM, Marijn Suijten wrote:
On 2023-05-12 11:00:22, Kuogee Hsieh wrote:

From: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>

Add DSC 1.2 hardware blocks to the catalog with necessary sub-block and
feature flag information.  Each display compression engine (DCE) contains
dual hard slice DSC encoders so both share same base address but with
its own different sub block address.

Can we have an explanation of hard vs soft slices in some commit message
and/or code documentation?


Not in this one. It wont look appropriate. I would rather remove "hard"
to avoid confusion.

That is totally fine, let's remove it instead.

<snip>
+	DSC_BLK_1_2("dce_0", DSC_0, 0x80000, 0x100, 0, dsc_sblk_0),

Downstream says that the size is 0x10 (and 0x100 for the enc sblk, 0x10
for the ctl sblk).  This simply fills it up to the start of the enc sblk
so that we can see all registers in the dump?  After all only
DSC_CMN_MAIN_CNF is defined in the main register space, so 0x10 is
adequate.


.len today is always only for the dump. and yes even here we have only
0x100 for the enc and 0x10 for the ctl.

+static const struct dpu_dsc_sub_blks dsc_sblk_0 = {
+	.enc = {.base = 0x100, .len = 0x100},
+	.ctl = {.base = 0xF00, .len = 0x10},
+};

The issue here is that, the dpu snapshot does not handle sub_blk parsing
today. Its a to-do item. So for that reason, 0x100 was used here to
atleast get the full encoder dumps.

But then you don't see the ENC block?  It starts at 0x100 (or 0x200) so
then the length should be longer... it should in fact depend on even/odd
DCE then?


You are right that the length should be longer. It should be 0x29c then and ctl blocks will not be included anyway.

The fundamental issue which remains despite increasing the length will be that the two blocks will print duplicate information. So dce_0_0 and dce_0_1 will print the same information twice as the base address is the same.

Odd/even DCE intelligence is not there in these macros and will be an overkill to just support the dump.

So overall, I dont think any of it is a good solution yet.

I think the best way to do this will be to add sub-block parsing support to the DPU devcoredump.

So what will happen is similar to downstream design in sde_dbg, when a block has sub-blocks we will respect the sub-block's len and not the parent block's as that will be more accurate.

If 0x29c is going to help the cause till then we can change it.


+	DSC_BLK_1_2("dce_0", DSC_1, 0x80000, 0x100, 0, dsc_sblk_1),

Should we add an extra suffix to the name to indicate which hard-slice
DSC encoder it is?  i.e. "dce_0_0" and "dce_0_1" etc?

Ok, that should be fine. We can add it.

Great, thanks!

+	DSC_BLK_1_2("dce_1", DSC_2, 0x81000, 0x100, BIT(DPU_DSC_NATIVE_422_EN), dsc_sblk_0),
+	DSC_BLK_1_2("dce_1", DSC_3, 0x81000, 0x100, BIT(DPU_DSC_NATIVE_422_EN), dsc_sblk_1),


See comment below about loose BIT() in features.

Responded below.

+};
+
   static const struct dpu_intf_cfg sm8350_intf[] = {
   	INTF_BLK("intf_0", INTF_0, 0x34000, 0x280, INTF_DP, MSM_DP_CONTROLLER_0, 24, INTF_SC7280_MASK,
   			DPU_IRQ_IDX(MDP_SSPP_TOP0_INTR, 24),
@@ -215,6 +227,8 @@ const struct dpu_mdss_cfg dpu_sm8350_cfg = {
   	.dspp = sm8350_dspp,
   	.pingpong_count = ARRAY_SIZE(sm8350_pp),
   	.pingpong = sm8350_pp,
+	.dsc = sm8350_dsc,
+	.dsc_count = ARRAY_SIZE(sm8350_dsc),

Count goes first **everywhere else**, let's not break consistency here.


the order of DSC entries is swapped for all chipsets. Please refer to
dpu_sc8180x_cfg, dpu_sm8250_cfg etc.

Thanks for confirming that this is not the case in a followup mail :)

So if you are talking about consistency, this is actually consistent
with whats present in other chipsets.

If you are very particular about this, then once this lands, you can
change the order for all of them in another change.

Same answer for all swap comments.
<snip>
+/*
+ * NOTE: Each display compression engine (DCE) contains dual hard
+ * slice DSC encoders so both share same base address but with
+ * its own different sub block address.
+ */
+#define DSC_BLK_1_2(_name, _id, _base, _len, _features, _sblk) \

There are no address values here so this comment doesn't seem very
useful, and it is already duplicated on every DSC block array, where the
duplication is more visible.  Drop the comment here?


_base is the address. So base address. Does that clarify things?

This is referring to the NOTE: comment above.  There's _base as address
here, yes, but there's no context here that it'll be used in duplicate
fashion, unlike the SoC catalog files.  The request is to just drop it
here as it adds no value.


The duplication is there. the base is same for both the entries with dce_0.

+static const struct dpu_dsc_cfg sc8280xp_dsc[] = {
+	DSC_BLK_1_2("dce_0", DSC_0, 0x80000, 0x100, 0, dsc_sblk_0),
+	DSC_BLK_1_2("dce_0", DSC_1, 0x80000, 0x100, 0, dsc_sblk_1),

Both the blks use 0x80000 as base address and the note is just telling that.

+	{\
+	.name = _name, .id = _id, \
+	.base = _base, .len = _len, \

The len is always 0x100 (downstream says 0x10), should we hardcode it
here and drop _len?  We can always add it back if a future revision
starts changing it, but that's not the case currently.

+	.features = BIT(DPU_DSC_HW_REV_1_2) | _features, \

We don't willy-nilly append bits like that: should there be global
feature flags?

So this approach is actually better. This macro is a DSC_1_2 macro so it
will have the 1.2 feature flag and other features like native_422
support of that encoder are ORed on top of it. Nothing wrong with this.

I agree it is better, but we seem to be very selective in whether to
stick to the "old" principles in DPU versus applying a new pattern that
isn't used elsewhere yet (i.e. your request to _not_ shuffle the order
of .dsc and .dsc_count assignment to match other .x and .x_count, and do
that in a future patch instead).  If we want to be consistent
everywhere, these should be #defines that we'll flatten out in a
followup if at all.


Yes, if it the order was already swapped, then we could have maintained it for this patch and cleaned all of them up together. Nothing wrong in that approach.

But I already clarified that was a mistake. The order of dsc and dsc_count is not swapped so I agreed to do that here. So where is the inconsistency?

Or is this the start of a new era where we expand those defines in-line
and drop them altogether?  I'd much prefer that but we should first
align on this direction (and then also make the switch globally in a
followup).


Its case by case. No need to generalize.

In this the feature flag ORed with the base feature flag of DSC_1_2
makes it more clear.

- Marijn



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