Re: [PATCH 09/11] usb: dwc2: Skip clock gating on Broadcom SoCs

[Jeremy Linton <jeremy.linton@arm.com>]

Hi,

On 7/5/24 10:21, Stefan Wahren wrote:
> Hi Jeremy,
> 
> Am 05.07.24 um 17:03 schrieb Lukas Wunner:
>> On Fri, Jul 05, 2024 at 12:22:33PM +0200, Stefan Wahren wrote:
>>> Am 05.07.24 um 10:48 schrieb Lukas Wunner:
>>>> The real question is whether BCM2848 platforms likewise cannot disable
>>>> the clock of the dwc2 controller or whether this is specific to the
>>>> BCM2835.  Right now dwc2_set_bcm_params() is applied to both the
>>>> BCM2848 and BCM2835.  If the BCM2848 behaves differently in this
>>>> regard, we'd have to duplicate dwc2_set_bcm_params() for the BCM2835.
>>>  From my understand BCM2848 refers to the same SoC, but the ACPI
>>> implementation uses a different ID [2]. So I think this is safe.
>>> [2] -
>>> https://patches.linaro.org/project/linux-usb/patch/20210413215834.3126447-2-jeremy.linton@arm.com/
>> Careful there, the patch vaguely says...
>>
>>      With that added and identified as "BCM2848",
>>      an id in use by other OSs for this device, the dw2
>>      controller on the BCM2711 will work.
>>
>> ...which sounds like they copy-pasted the BCM2848 id from somewhere else.
>> I would assume that BCM2848 is really a different SoC and not just
>> a different name for the BCM2835, but hopefully BroadCom folks will
>> be able to confirm or deny this (and thus the necessity of the quirk
>> on BCM2848 and not just on BCM2835).
> could you please clarify this situation?

This id comes from the edk2-platforms ACPI tables and is currently used 
by both the rpi3 and rpi4, and AFAIK nothing else as the rpi5-dev work 
is currently only exposing XHCI.

The ID is strictly the USB controller not the SoC. Its a bit confusingly 
named, but something we inherited from the much older windows/edk2 port, 
where it appears that the peripheral HID's were just picked in numerical 
order.

[0] 
https://github.com/tianocore/edk2-platforms/blob/12f68d29abdc9d703f67bd743fdec23ebb1e966e/Platform/RaspberryPi/AcpiTables/GpuDevs.asl#L15