Re: [PATCH v9 04/10] usb: dwc3: core: Skip setting event buffers for host only controllers

[Thinh Nguyen]

On Mon, Jun 26, 2023, Thinh Nguyen wrote:
> On Sat, Jun 24, 2023, Krishna Kurapati PSSNV wrote:
> > 
> > 
> > On 6/24/2023 3:57 AM, Thinh Nguyen wrote:
> > > On Wed, Jun 21, 2023, Krishna Kurapati wrote:
> > > > On some SoC's like SA8295P where the tertiary controller is host-only
> > > > capable, GEVTADDRHI/LO, GEVTSIZ, GEVTCOUNT registers are not accessible.
> > > > Trying to access them leads to a crash.
> > > > 
> > > > For DRD/Peripheral supported controllers, event buffer setup is done
> > > > again in gadget_pullup. Skip setup or cleanup of event buffers if
> > > > controller is host-only capable.
> > > > 
> > > > Suggested-by: Johan Hovold <johan@xxxxxxxxxx>
> > > > Signed-off-by: Krishna Kurapati <quic_kriskura@xxxxxxxxxxx>
> > > > ---
> > > >   drivers/usb/dwc3/core.c | 11 +++++++++++
> > > >   1 file changed, 11 insertions(+)
> > > > 
> > > > diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> > > > index 32ec05fc242b..e1ebae54454f 100644
> > > > --- a/drivers/usb/dwc3/core.c
> > > > +++ b/drivers/usb/dwc3/core.c
> > > > @@ -486,6 +486,11 @@ static void dwc3_free_event_buffers(struct dwc3 *dwc)
> > > >   static int dwc3_alloc_event_buffers(struct dwc3 *dwc, unsigned int length)
> > > >   {
> > > >   	struct dwc3_event_buffer *evt;
> > > > +	unsigned int hw_mode;
> > > > +
> > > > +	hw_mode = DWC3_GHWPARAMS0_MODE(dwc->hwparams.hwparams0);
> > > > +	if (hw_mode == DWC3_GHWPARAMS0_MODE_HOST)
> > > > +		return 0;
> > > 
> > > This is a little awkward. Returning 0 here indicates that this function
> > > was successful, and the event buffers were allocated based on the
> > > function name. Do this check outside of dwc3_alloc_one_event_buffer()
> > > and specifically set dwc->ev_buf = NULL if that's the case.
> > > 
> > Hi Thinh,
> > 
> >   Apologies, I didn't understand the comment properly.
> > 
> >   I thought we were supposed to return 0 here if we fulfill the goal of this
> > function (allocate if we are drd/gadget and don't allocate if we are host
> > mode only).
> 
> The name of the function implies that it returns 0 if it allocated the
> event buffer. If there are multiple conditions to the function returning
> 0 here, then we should document it.
> 
> > 
> >   If we return a non zero error here, probe would fail as this call will be
> > done only for host only controllers during probe and nowhere else.
> > 
> >   Are you suggesting we move this check to dwc3_alloc_one_event_buffer call
> > ?
> > 
> > Regards,
> > Krishna,
> > 
> 
> I'm suggesting to move the check to the caller of
> dwc3_alloc_one_event_buffer(). Something like this so that it's
> self-documented:
> 
> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> index 0beaab932e7d..bba82792bf6f 100644
> --- a/drivers/usb/dwc3/core.c
> +++ b/drivers/usb/dwc3/core.c
> @@ -1773,6 +1773,7 @@ static int dwc3_probe(struct platform_device *pdev)
>  	struct resource		*res, dwc_res;
>  	void __iomem		*regs;
>  	struct dwc3		*dwc;
> +	unsigned int		hw_mode;
>  	int			ret;
>  
>  	dwc = devm_kzalloc(dev, sizeof(*dwc), GFP_KERNEL);
> @@ -1854,11 +1855,16 @@ static int dwc3_probe(struct platform_device *pdev)
>  
>  	pm_runtime_forbid(dev);
>  
> -	ret = dwc3_alloc_event_buffers(dwc, DWC3_EVENT_BUFFERS_SIZE);
> -	if (ret) {
> -		dev_err(dwc->dev, "failed to allocate event buffers\n");
> -		ret = -ENOMEM;
> -		goto err_allow_rpm;
> +	hw_mode = DWC3_GHWPARAMS0_MODE(dwc->hwparams.hwparams0);
> +	if (hw_mode == DWC3_GHWPARAMS0_MODE_HOST) {
> +		dwc->ev_buf = NULL;
> +	} else {
> +		ret = dwc3_alloc_event_buffers(dwc, DWC3_EVENT_BUFFERS_SIZE);
> +		if (ret) {
> +			dev_err(dwc->dev, "failed to allocate event buffers\n");
> +			ret = -ENOMEM;
> +			goto err_allow_rpm;
> +		}
>  	}
>  
>  	dwc->edev = dwc3_get_extcon(dwc);
> 

Actually, please ignore. there's already a document there, I missed that
for some reason. What you did is fine. Though, I don't see the condition
for ev_buf = NULL anywhere. Can you add that for clarity?

Thanks,
Thinh