Re: [PATCH V3 4/6] usb: ohci-platform: Add support for Broadcom STB SoC's

[Al Cooper]

On 11/7/18 12:29 PM, Florian Fainelli wrote:
> On 11/7/18 8:27 AM, Alan Stern wrote:
> > On Wed, 7 Nov 2018, Al Cooper wrote:
> >
> > > On 11/7/18 10:23 AM, Alan Stern wrote:
> > > > On Tue, 6 Nov 2018, Florian Fainelli wrote:
> > > >
> > > > > On 11/6/18 1:40 PM, Al Cooper wrote:
> > > > > > On 11/6/18 11:08 AM, Alan Stern wrote:
> > > > > > > On Mon, 5 Nov 2018, Al Cooper wrote:
> > > > > > >
> > > > > > > > Add support for Broadcom STB SoC's to the ohci platform driver.
> > > > > > > >
> > > > > > > > Signed-off-by: Al Cooper <alcooperx@xxxxxxxxx>
> > > > > > > > ---
> > > > > > >
> > > > > > > > @@ -177,6 +189,8 @@ static int ohci_platform_probe(struct
> > > > > > > > platform_device *dev)
> > > > > > > >   ÂÂÂÂÂÂÂÂÂ ohci->flags |= OHCI_QUIRK_FRAME_NO;
> > > > > > > >   ÂÂÂÂÂ if (pdata->num_ports)
> > > > > > > >   ÂÂÂÂÂÂÂÂÂ ohci->num_ports = pdata->num_ports;
> > > > > > > > +ÂÂÂ if (pdata->suspend_without_phy_exit)
> > > > > > > > +ÂÂÂÂÂÂÂ hcd->suspend_without_phy_exit = 1;
> > > > > > >
> > > > > > > Sorry if I missed this in the earlier discussions... Is there any
> > > > > > > possibility of adding a DT binding that could express this requirement,
> > > > > > > instead of putting it in the platform data?
> > > > > > >
> > > > > > > Alan Stern
> > > > > >
> > > > > > Alan,
> > > > > >
> > > > > > That was my original approach but internal review suggested that I use
> > > > > > pdata instead. Below is my original patch for:
> > > > >
> > > > > And the reason for that suggestion was really because it was percevied
> > > > > as encoding a driver behavior as a Device Tree property as opposed to
> > > > > describing something that was inherently and strictly a hardware
> > > > > behavior (therefore suitable for Device Tree).
> > > >
> > > > Right.  The best way to approach this problem is to identify and
> > > > characterize the hardware behavior which makes this override necessary.
> > > > Then _that_ can be added to DT, since it will be a property of the
> > > > hardware rather than of the driver.
> > > >
> > > > > > Add the ability to skip calling the PHY's exit routine on suspend
> > > > > > and the PHY's init routine on resume. This is to handle a USB PHY
> > > > > > that should have it's power_off function called on suspend but cannot
> > > > > > have it's exit function called because on exit it will disable the
> > > > > > PHY to the point where register accesses to the Host Controllers
> > > > > > using the PHY will be disabled and the host drivers will crash.
> > > >
> > > > What's special about this PHY?  Why does the exit function mess the PHY
> > > > up?  Or to put it another way, why doesn't the exit function mess up
> > > > other PHYs in the same way?
> > > >
> > > > For that matter, can we change the code so that suspend doesn't call
> > > > the exit function for _any_ PHY?  Will just calling the power_off
> > > > function be good enough?  If not, then why not?
> > > >
> > > > Alan Stern
> > >
> > > In our USB hardware the USB PHY supplies a clock for the EHCI/OHCI and
> > > XHCI host controllers and if the PHY is totally shut down the EHCI, OHCI
> > > and XHCI registers will cause an exception if accessed and cause the
> > > EHCI, OHCI and XHCI drivers to crash. There is always talk of fixing
> > > this in the hardware by adding an aux clock that will takeover when the
> > > PHY clock is shut down, but this hasn't happened yet. It seems like
> > > "exit on suspend" still makes sense on systems that don't have this
> > > problem (additional power savings?) so removing the exit on suspend for
> > > all systems is not a good idea.
> >
> > Then in theory you should be able to add a Device Tree property which
> > says that the PHY provides a clock for the USB host controller.  That
> > is strictly a property of the hardware; it has nothing to do with the
> > driver.  Therefore it is appropriate for DT.
>
> The very compatible string that is being allocated/defined for this
> controller carries that information already, that is, if you probe a
> "brcm,bcm7445-ohci" compatible then that means the controller has a
> dependency on the PHY to supply its clock.
>
> Adding a property vs. keying on the compatible string makes sense if you
> know there is at least a second consumer of that property (unless we
> make it a broadcom specific property, in which case, it really is
> redundant with the compatible string).
>
> Anyway, my grudge with that property was the name chosen initially,
> which included an action to be performed by an implementation as opposed
> to something purely descriptive. E.g: 'phy-supplies-clock' might be okay.
>
> > Wouldn't this solve your issue?
>
> It would not change much except that there is no need to much with
> ohci-platform.c anymore, but ultimately that property needs to be read
> by ohci-hcd.c and acted on, which would likely lead to the same amount
> of changes as those present in patch #2 currently.
We also need this functionality in the EHCI and XHCI drivers and it's 
not the ohci-hcd.c module that needs to know, it's the core/phy.c module 
called from core/hcd.c.

Al