linux-kernel - Re: [PATCH 2/2] drm/tidss: Add support for AM62L display subsystem

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Message-ID: <f6b20a29-1205-4f5e-87b6-fec58bd43545@ideasonboard.com>
Date: Wed, 5 Feb 2025 08:56:53 +0200
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Devarsh Thakkar <devarsht@...com>
Cc: "Bajjuri, Praneeth" <praneeth@...com>,
 "Raghavendra, Vignesh" <vigneshr@...com>, "Jain, Swamil" <s-jain1@...com>,
 "Donadkar, Rishikesh" <r-donadkar@...com>,
 "Choudhary, Jayesh" <j-choudhary@...com>,
 "Shenoy, Harikrishna" <h-shenoy@...com>,
 Aradhya Bhatia <aradhya.bhatia@...ux.dev>,
 "jyri.sarha@....fi" <jyri.sarha@....fi>,
 "airlied@...il.com" <airlied@...il.com>,
 "maarten.lankhorst@...ux.intel.com" <maarten.lankhorst@...ux.intel.com>,
 "mripard@...nel.org" <mripard@...nel.org>,
 "tzimmermann@...e.de" <tzimmermann@...e.de>,
 "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
 "simona@...ll.ch" <simona@...ll.ch>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
 "robh@...nel.org" <robh@...nel.org>, "krzk+dt@...nel.org"
 <krzk+dt@...nel.org>, "conor+dt@...nel.org" <conor+dt@...nel.org>
Subject: Re: [PATCH 2/2] drm/tidss: Add support for AM62L display subsystem

Hi,

On 05/02/2025 07:53, Devarsh Thakkar wrote:
> Hi Tomi
> 
>>> Thanks for pointing out, I probably missed this since the use-case still
>>> worked since VP interrupts were still enabled and those were sufficient to
>>> drive the display
>>> but the VID underflow interrupts and VID specific bits were probably not
>>> enabled at-all due to above miss, so agreed
>>> we should probably go ahead with a different reg space for AM62L due to
>>> aforementioned differences.
>>
>> I think I disagree here. Afaiu, AM62L has plane at hw index 1 (VIDL1), but the
>> plane at hw index 0 (VID1) is not instantiated in the hardware. But the
>> registers are the same, i.e. AM62L's registers for VIDL1 match AM65x/AM62x
>> registers, right?
>>
>> If so, we just need to tell the driver the hw index, instead of creating new
>> register offsets as done in v2.
>>
>> Or am I missing something here? (I haven't looked at the HW manual yet).
>>
> 
> No that's not the only difference. For AM62L, the VID_IRQENABLE/STATUS
> registers start at +0x4 as compared to AM65x/AM62x/ :
> 
> AM62L:
>          [DISPC_VID_IRQENABLE_OFF] =             0x48,
> 
>          [DISPC_VID_IRQSTATUS_OFF] =             0x5c,
> 
> AM62x/AM65x:
> 
>          [DISPC_VID_IRQENABLE_OFF] =             0x44,
> 
>          [DISPC_VID_IRQSTATUS_OFF] =             0x58,

But they actually don't start at different offsets.

AM62L TRM has:

DSS_COMMON_VID_IRQENABLE_1  3020 0048h
DSS_COMMON_VID_IRQSTATUS_1  3020 005Ch

AM65X TRM has:

DSS0_COMMON_VID_IRQENABLE_1  04A0 0048h
DSS0_COMMON_VID_IRQSTATUS_1  04A0 005Ch

It's just that on AM62L the VID0 isn't instantiated in the hardware. 
VID1 is at the same place.

  Tomi