Message-ID: <ed82e498-b3af-46f6-97ce-3a2f47872935@ideasonboard.com>
Date: Fri, 2 May 2025 13:55:50 +0300
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Devarsh Thakkar <devarsht@...com>
Cc: praneeth@...com, vigneshr@...com, aradhya.bhatia@...ux.dev,
 s-jain1@...com, r-donadkar@...com, j-choudhary@...com, h-shenoy@...com,
 jyri.sarha@....fi, airlied@...il.com, maarten.lankhorst@...ux.intel.com,
 mripard@...nel.org, tzimmermann@...e.de, dri-devel@...ts.freedesktop.org,
 simona@...ll.ch, linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
 robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org
Subject: Re: [PATCH v5 2/3] drm/tidss: Update infrastructure to support K3 DSS
 cut-down versions

Hi,

On 02/05/2025 13:47, Devarsh Thakkar wrote:
> Hi Tomi,
> 
> Thanks for the quick revert.
> 
> On 02/05/25 13:37, Tomi Valkeinen wrote:
>> Hi,
>>
>> On 02/05/2025 10:06, Devarsh Thakkar wrote:
>>> Hi Tomi
>>>
>>> Thanks for quick comments.
>>>
>>> On 30/04/25 23:12, Tomi Valkeinen wrote:
>>>> On 30/04/2025 19:37, Devarsh Thakkar wrote:
>>>>> Hi Tomi
>>>>>
>>>>> Thanks for the review.
>>>>>
>>>>> <snip>
>>>>>>>      @@ -2025,7 +2101,7 @@ int dispc_plane_check(struct dispc_device
>>>>>>> *dispc, u32 hw_plane,
>>>>>>>                    const struct drm_plane_state *state,
>>>>>>>                    u32 hw_videoport)
>>>>>>>      {
>>>>>>> -    bool lite = dispc->feat->vid_lite[hw_plane];
>>>>>>> +    bool lite = dispc->feat->vid_info[hw_plane].is_lite;
>>>>>>
>>>>>> I don't think this is correct. You can't access the vid_info[] with
>>>>>> the
>>>>>> hw-id.
>>>>>
>>>>> I don't think hw_id is getting passed to hw_plane here. The
>>>>> dispc_plane_check is called from tidss_plane_atomic_check which passes
>>>>> hw_plane as tplane->hw_plane_id and this index starts from actually
>>>>> instantiated planes i.e. from 0 and are contiguous as these are
>>>>
>>>> Well, if tplane->hw_plane_id is not the HW plane id (i.e. it's misnamed
>>>> now), and tidss_plane.c calls dispc_plane_enable() with tplane-
>>>>> hw_plane_id as the hw_plane parameter, which is used as a HW plane
>>>> ID... Then... One of these is wrong, no?
>>>>
>>>
>>> As mentioned here [1], dispc_plane_enable acts on VID_* registers which
>>> are only mapped per the instantiated/actual pipes present in the SoC, so
>>> the indexing always starts from 0 and we need not worry about skipping
>>> un-instantiated planes.
>>>
>>> So hw_plane_id -> Index of only instantiated planes starting from 0
>>> hw_id -> Hardware Index taking into account instantiated +
>>> un-instantiated/skipped planes main used for common0/1 region registers
>>> dealing with VID planes.
>>>
>>>
>>> For e.g. for AM62L which includes VIDL pipe
>>> hw_plane_id -> 0
>>> hw_id -> 1
>>>
>>>
>>>>> populated from vid_order array (hw_plane_id =
>>>>> feat->vid_order[tidss->num_planes];) and not the hw_id index.
>>>>>
>>>>> So for e.g. for AM62L even though hw_id is 1 for VIDL hw_plane is
>>>>> getting passed as 0 and that's how it is able to access the first and
>>>>> only member of vid_info struct and read the properties correctly and
>>>>> function properly as seen in test logs [1].
>>>>
>>>> If for AM62L the tplane->hw_plane_id is 0, the the dispc_plane_enable()
>>>> call would enable the wrong plane, wouldn't it?
>>>>
>>>> But even if it all works, I think this highlights how confusing it is...
>>>>
>>>>>
>>>>>>
>>>>>>>          u32 fourcc = state->fb->format->format;
>>>>>>>          bool need_scaling = state->src_w >> 16 != state->crtc_w ||
>>>>>>>              state->src_h >> 16 != state->crtc_h;
>>>>>>> @@ -2096,7 +2172,7 @@ void dispc_plane_setup(struct dispc_device
>>>>>>> *dispc, u32 hw_plane,
>>>>>>>                     const struct drm_plane_state *state,
>>>>>>>                     u32 hw_videoport)
>>>>>>>      {
>>>>>>> -    bool lite = dispc->feat->vid_lite[hw_plane];
>>>>>>> +    bool lite = dispc->feat->vid_info[hw_plane].is_lite;
>>>>>>
>>>>>> Here too.
>>>>>
>>>>> Here also hw_plane is getting passed as 0 and not the hw_id which is 1
>>>>> for AM62L.
>>>>>
>>>>>>
>>>>>>>          u32 fourcc = state->fb->format->format;
>>>>>>>          u16 cpp = state->fb->format->cpp[0];
>>>>>>>          u32 fb_width = state->fb->pitches[0] / cpp;
>>>>>>> @@ -2210,7 +2286,7 @@ static void dispc_k2g_plane_init(struct
>>>>>>> dispc_device *dispc)
>>>>>>>          /* MFLAG_START = MFLAGNORMALSTARTMODE */
>>>>>>>          REG_FLD_MOD(dispc, DISPC_GLOBAL_MFLAG_ATTRIBUTE, 0, 6, 6);
>>>>>>>      -    for (hw_plane = 0; hw_plane < dispc->feat->num_planes;
>>>>>>> hw_plane++) {
>>>>>>> +    for (hw_plane = 0; hw_plane < dispc->feat->num_vids;
>>>>>>> hw_plane++) {
>>>>>>>              u32 size = dispc_vid_get_fifo_size(dispc, hw_plane);
>>>>>>>              u32 thr_low, thr_high;
>>>>>>>              u32 mflag_low, mflag_high;
>>>>>>> @@ -2226,7 +2302,7 @@ static void dispc_k2g_plane_init(struct
>>>>>>> dispc_device *dispc)
>>>>>>>                dev_dbg(dispc->dev,
>>>>>>>                  "%s: bufsize %u, buf_threshold %u/%u, mflag threshold
>>>>>>> %u/%u preload %u\n",
>>>>>>> -            dispc->feat->vid_name[hw_plane],
>>>>>>> +            dispc->feat->vid_info[hw_plane].name,
>>>>>>
>>>>>> Here hw_plane is not actually the hw-id (anymore), but elsewhere in
>>>>>> this
>>>>>> function it is used as a hw-id, which is no longer correct.
>>>>>
>>>>> For accessing vid_info hw_plane needs to be used which is the index of
>>>>> actually instantiated planes and I see it as correctly being passed for
>>>>> AM62L too. hw_id is only for dispc_k3_vid* functions where we need to
>>>>> skip the not-instantiated vid regions by adding the offset per the
>>>>> hw_id
>>>>> index.
>>>>
>>>> Hmm, sorry, I don't follow. If we use the same variable, hw_plane, to
>>>> access the vid_info[], and as a parameter to functions that take
>>>> hw_plane, e.g., dispc_vid_set_buf_threshold(), isn't one of those uses
>>>> wrong?
>>>>
>>>> Oh, wait... I think I see it now. For some functions using the hw_id as
>>>> the hw_plane parameter is fine, as they access the VID's registers by
>>>> just using, e.g. dispc_vid_write(), which gets the address correctly
>>>> from dispc->base_vid[hw_plane], as that one is indexed from 0 to
>>>> num_vids.
>>>>
>>>
>>> Yes exactly.
>>>
>>>> But some functions use registers that have bits based on the hw_id (like
>>>> dispc_k3_vid_write_irqstatus), and then we use the hw_id for the
>>>> hw_plane parameter. If that function were to also write a vid register,
>>>> using the passed hw_plane, it wouldn't work, but I guess we don't do
>>>> that.
>>>>
>>>
>>> Yes, hw_id is only for dispc_k3_vid* functions dealing with common
>>> region registers that play with VID pipes.
>>>
>>>> It feels broken... We can't have 'hw_plane' that's sometimes the HW id
>>>> (i.e. 1 for AM62L), and sometimes the driver's index (i.e. 0 for AM62L).
>>>>
>>>
>>> Sorry I don't follow, what exactly is broken here. hw_plane is for
>>> instantiated planes present in SoC used in context of VID* register
>>> space while doing reg writess and hw_id is the plane hardware index
>>> w.r.t larger K3 family i.e used in context for common register space.
>>
>> We have, as an example, these two functions:
>>
>> void dispc_plane_enable(struct dispc_device *dispc, u32 hw_plane, bool
>> enable)
>>
>> static void dispc_k3_vid_write_irqstatus(struct dispc_device *dispc, u32
>> hw_plane, dispc_irq_t vidstat)
>>
>> When the caller calls these functions on AM62L, what does it provide in
>> 'hw_plane' when it wants to enable the first plane of write the
>> irqstatus for the first plane?
> 
> It uses hw_id i.e. 1 for all vid irqstatus related registers since it is
> accessing am65x common region register space which has vid on idx0 which
> we want to skip for am62l.
> 
> For dispc_plane_enable(), the caller uses
>> 0, for dispc_k3_vid_write_irqstatus(), the caller uses 1...
> 
> Yes above is correct, and I think that's how it is supposed to be.

No it's not. Both functions have "hw_plane" parameter, yet they require 
a different value to be used even when referring to the same plane.

>> With a quick look at the code, changing the callers to pass the "old
>> style" hw_plane as the parameter to those irq functions, and the
>> functions internally get the hw_id, would solve most of the problems.
> 
> I don't follow above, hw_plane has 0 so it should not be used for
> programming irq related functions which expect idx 1 as explained above.

We have various functions in tidss_dispc.c that have hw_plane as a 
parameter. But the caller is supposed to know that for some functions 
hw_plane is a plane index from 0, and for some it's the hw_id from 
vid_info[].

>> There's still dispc_k3_set_irqenable() which manages 'main_disable' and
>> needs the hw_id, but maybe that's fine, even if a bit confusing.
>>
> 
> I still feel there is no inherent bug here, but let me know if you want
> me to put some debug prints or get register dump so that we can double
> confirm.

I'm not saying there's a bug. I'm saying it's bad code and will cause 
confusion and bugs in the future.

  Tomi

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