linux-kernel - Re: [PATCH 3/3] usb: dwc2: prevent core phy initialisation

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Date:   Fri, 9 Dec 2022 12:15:34 +0100
From:   Quentin Schulz <quentin.schulz@...obroma-systems.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Quentin Schulz <foss+kernel@...il.net>
Cc:     Minas Harutyunyan <hminas@...opsys.com>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        William Wu <william.wu@...k-chips.com>,
        Bin Yang <yangbin@...k-chips.com>,
        Frank Wang <frank.wang@...k-chips.com>
Subject: Re: [PATCH 3/3] usb: dwc2: prevent core phy initialisation

Hi Greg,

On 12/8/22 16:53, Greg Kroah-Hartman wrote:
> On Wed, Dec 07, 2022 at 02:19:18PM +0100, Quentin Schulz wrote:
>> From: Bin Yang <yangbin@...k-chips.com>
>>
>> The usb phys need to be controlled dynamically on some Rockchip SoCs.
>> So set the new HCD flag which prevents USB core from trying to manage
>> our phys.
>>
>> Signed-off-by: Bin Yang <yangbin@...k-chips.com>
>> Signed-off-by: Frank Wang <frank.wang@...k-chips.com>
>> Signed-off-by: Quentin Schulz <quentin.schulz@...obroma-systems.com>
>> ---
>>   drivers/usb/dwc2/hcd.c | 7 +++++++
>>   1 file changed, 7 insertions(+)
>>
>> diff --git a/drivers/usb/dwc2/hcd.c b/drivers/usb/dwc2/hcd.c
>> index 657f1f659ffaf..757a66fa32fa8 100644
>> --- a/drivers/usb/dwc2/hcd.c
>> +++ b/drivers/usb/dwc2/hcd.c
>> @@ -5315,6 +5315,13 @@ int dwc2_hcd_init(struct dwc2_hsotg *hsotg)
>>   	if (!IS_ERR_OR_NULL(hsotg->uphy))
>>   		otg_set_host(hsotg->uphy->otg, &hcd->self);
>>   
>> +	/*
>> +	 * do not manage the PHY state in the HCD core, instead let the driver
>> +	 * handle this (for example if the PHY can only be turned on after a
>> +	 * specific event)
>> +	 */
>> +	hcd->skip_phy_initialization = 1;
> 
> Wait, doesn't this mess with the phy logic for all other chips that use
> this IP block?  Have you tested this on other systems?
> 

I have not. I asked this in the cover-letter but I guess I should have 
made the patch series an RFC for this reason?

> I'd like some verification first before taking this change as it seems
> very specific-platform.
> 

There's already some platform-specific callbacks for the driver (see
dwc2_set_rk_params in drivers/usb/dwc2/params.c) but this gets called 
too early, before hcd structure is actually allocated. So we either need 
to use some "proxy"/shadow variable in dwc2_core_params and then update 
it right after hcd gets allocated or have another platform-specific 
callback only for hcd (post-)initialization.

Nothing too fancy so shouldn't take too long to implement. Any 
preference? Something else?

Also on a side note, after further testing, USB peripheral mode in 
dual-role mode does not seem to be entirely fixed with this patch 
series, I still have occasional locks. But considering that it 
absolutely didn't work before, it is some kind of progress.
There are also some issues related to USB host mode in dual-role mode 
but I saw those happening before the patch series too. I'll see what I 
can do, really frustrating to work with IPs for which there's no 
documentation :/

Cheers,
Quentin