Re: [PATCH v8 3/9] usb: dwc3: core: Access XHCI address space temporarily to read port info

[Krishna Kurapati PSSNV]

On 5/17/2023 1:05 PM, Johan Hovold wrote:

> > > You should not make another copy of xhci_find_next_ext_cap(), but rather
> > > use it directly.
> > >
> > > We already have drivers outside of usb/host using this function so it
> > > should be fine to do the same for now:
> > >
> > > 	#include "../host/xhci-ext-caps.h"
>
> >     This was the approach which we followed when we first introduced the
> > patch [1]. But Thinh suggested to duplicate code so that we can avoid
> > any dependency on xhci (which seems to be right). So since its just one
> > function, I duplicated it here.
>
> Ok, fair enough. I still think we should not be duplicating the
> xhci definitions like this even if we were to copy the helper to avoid
> any future dependencies on xhci (it's currently an inline function,
> which is also not very nice).
>
> I'll take closer look at the rest of the series as there are a few more
> of these layering violations which we should try to avoid.
>
> > > > +	offset = dwc3_xhci_find_next_ext_cap(regs, 0,
> > > > +					XHCI_EXT_CAPS_PROTOCOL);
> > > > +	while (offset) {
>
> > > > +		temp = readl(regs + offset);
> > > > +		major_revision = XHCI_EXT_PORT_MAJOR(temp);
> > > > +
> > > > +		temp = readl(regs + offset + 0x08);
>
> > > > +		if (major_revision == 0x03) {
> > > > +			dwc->num_usb3_ports += XHCI_EXT_PORT_COUNT(temp);
> > > > +		} else if (major_revision <= 0x02) {
> > > > +			dwc->num_usb2_ports += XHCI_EXT_PORT_COUNT(temp);
> > > > +		} else {
> > > > +			dev_err(dwc->dev,
> > > > +				"Unrecognized port major revision %d\n", major_revision);
>
> > > Perhaps this should be handles as in xhci core by simply warning and
> > > continuing instead.
> > I broke the loop and went to unmap as we are not sure what values would
> > be read. Any use of continuing ?
>
> Mostly to align with xhci core which currently handles this case. It
> would not not work unless you get rid of the max-ports check below
> though.
>   
> > > > +			ret = -EINVAL;
> > > > +			goto unmap_reg;
> > > > +		}
> > > > +
> > > > +		offset = dwc3_xhci_find_next_ext_cap(regs, offset,
> > > > +						XHCI_EXT_CAPS_PROTOCOL);
> > > > +	}
> > > > +
> > > > +	temp = readl(regs + DWC3_XHCI_HCSPARAMS1);
> > > > +	if (HCS_MAX_PORTS(temp) != (dwc->num_usb3_ports + dwc->num_usb2_ports)) {
> > > > +		dev_err(dwc->dev,
> > > > +			"Mismatched reported MAXPORTS (%d)\n", HCS_MAX_PORTS(temp));
> > > > +		ret = -EINVAL;
> > > > +		goto unmap_reg;
> > > > +	}
> > >
> > > Not sure this is needed either.
> > >
> > > Could this risk regressing platforms which does not have currently have
> > > all PHYs described in DT?
> > No, it doesn't. AFAIK, this only tells how many ports are present as per
> > the core consultant configuration of the device. I tried to explain what
> > would happen incase phy's are not present in DT in [2] & [3].
>
> Right, whether the PHYs are described in DT is not directly related to
> this.
>
> As long as HCS_MAX_PORTS by definition (assumption) is always
> (dwc->num_usb3_ports + dwc->num_usb2_ports) any such machines would
> continue to work.
>
> But if you want to catch machines where this assumption does not hold,
> you could also end up regressing machines which have so far been working
> despite these numbers not adding up.
>
> That may be acceptable, but I'm still not sure what the value of this
> check is (e.g. as xhci core will handle basic sanity checks like usb2 +
> usb3 <= max_ports).

Hi Johan,

  Thanks for the review comments. Ideally the HCC_PARAMS1 must indicate 
total number of ports supported. If not then I believe the core 
consultant configuration is wrong.

According to the spec:

"The MaxPorts value in the HCSPARAMS1 register defines the number of
Port Register Sets (e.g. PORTSC, PORTPMSC, and PORTLI register sets)."

So shouldn't the (usb2+usb3 ports be equal to MaxPorts to ensure each 
port properly accesses the respective PortSC etc., ?

Do we have any machines today that support HOST_ONLY_CONFIG indicated in 
HWPARAMS0 that support multiport and violate this rule ?

Regards,
Krishna,