Re: [PATCH v5 1/2] usb: ulpi: defer ulpi_register on ulpi_read_id timeout

[Ferry Toth]

Op 21-12-2022 om 18:30 schreef Guenter Roeck:
> On Wed, Dec 21, 2022 at 03:29:09PM +0100, Ferry Toth wrote:
> > Hi
> >
> > On 21-12-2022 13:41, Guenter Roeck wrote:
> > > On Wed, Dec 21, 2022 at 11:07:50AM +0100, Ferry Toth wrote:
> > > > Hi,
> > > >
> > > > On 20-12-2022 20:43, Guenter Roeck wrote:
> > > > > On Mon, Dec 05, 2022 at 09:15:26PM +0100, Ferry Toth wrote:
> > > > > > Since commit 0f0101719138 ("usb: dwc3: Don't switch OTG -> peripheral
> > > > > > if extcon is present") Dual Role support on Intel Merrifield platform
> > > > > > broke due to rearranging the call to dwc3_get_extcon().
> > > > > >
> > > > > > It appears to be caused by ulpi_read_id() on the first test write failing
> > > > > > with -ETIMEDOUT. Currently ulpi_read_id() expects to discover the phy via
> > > > > > DT when the test write fails and returns 0 in that case, even if DT does not
> > > > > > provide the phy. As a result usb probe completes without phy.
> > > > > >
> > > > > > Make ulpi_read_id() return -ETIMEDOUT to its user if the first test write
> > > > > > fails. The user should then handle it appropriately. A follow up patch
> > > > > > will make dwc3_core_init() set -EPROBE_DEFER in this case and bail out.
> > > > > >
> > > > > > Fixes: ef6a7bcfb01c ("usb: ulpi: Support device discovery via DT")
> > > > > > Cc: stable@xxxxxxxxxxxxxxx
> > > > > > Signed-off-by: Ferry Toth <ftoth@xxxxxxxxxxxxxx>
> > > > > Hi,
> > > > >
> > > > > this patch results in some qemu test failures, specifically xilinx-zynq-a9
> > > > > machine and zynq-zc702 as well as zynq-zed devicetree files, when trying
> > > > > to boot from USB drive. The log shows
> > > > I'm not familiar with that platform. Does it use dt to discover the ulpi
> > > > device?
> > > The dt usb description includes
> > >
> > > 	usb_phy0: phy0 {
> > >                   compatible = "usb-nop-xceiv";
> > >                   #phy-cells = <0>;
> > >           };
> > >
> > > ...
> > >
> > > &usb0 {
> > >           status = "okay";
> > >           dr_mode = "host";
> > >           usb-phy = <&usb_phy0>;
> > > };
> > >
> > > ...
> > >
> > >                   usb0: usb@e0002000 {
> > >                           compatible = "xlnx,zynq-usb-2.20a", "chipidea,usb2";
> > >                           status = "disabled";
> > >                           clocks = <&clkc 28>;
> > >                           interrupt-parent = <&intc>;
> > >                           interrupts = <0 21 4>;
> > >                           reg = <0xe0002000 0x1000>;
> > >                           phy_type = "ulpi";
> > >                   };
> > >
> > > The chipidea core initialization code includes
> > >
> > >           if (!platdata->phy_mode)
> > >                   platdata->phy_mode = of_usb_get_phy_mode(dev->of_node);
> > >
> > > Does that mean that every chipidea based usb implementation specifying
> > > 	phy_type = "ulpi";
> > > in their devicetree description will now fail, plus maybe others
> > > who determine the phy mode from devicetree ?
> > I don't think so.
> > > > I'm guessing that the problem is actually caused by "usb: ulpi: defer
> > > > ulpi_register on ulpi_read_id timeout".
> > > Confused. Isn't that this patch ?
> > Ehem. Yes.
> > > > ulpi_read_id() now returns ETIMEDOUT due to the test write ulpi_write(ulpi,
> > > > ULPI_SCRATCH, 0xaa) failing.
> > > >
> > > > Maybe  we can create a fix by skipping the test write in case dt discovery
> > > > is available and calling of_device_request_module() directly, instead of
> > > > masking the timed out test write as it was before?
> > > I have no idea. All I can see is that it appears that there was a reason
> > > for not returning an error if that test write failed.
> >
> > It seems to have been a quick patch to solve a power sequencing issue:
> >
> > "The ULPI bus code supports native enumeration by reading the
> > vendor ID and product ID registers at device creation time, but
> > we can't be certain that those register reads will succeed if the
> > phy is not powered up. To avoid any problems with reading the ID
> > registers before the phy is powered we fallback to DT matching
> > when the ID reads fail.
> >
> > If the ULPI spec had some generic power sequencing for these
> > registers we could put that into the ULPI bus layer and power up
> > the device before reading the ID registers. Unfortunately this
> > doesn't exist and the power sequence is usually device specific.
> > By having the device matched up with DT we can avoid this
> > problem."
> >
> > But as is, the code now requires a DT when there is a power
> > sequencing issue, which is wrong for Merrifield. It seems my patch
> > breaks the OF path, by replacing that by a deferred probe.
> >
> > I'm thinking the correct way would be:
> > - if present use DT
> > - else if test write fails, defer probe
> > - else enumeration by reading the vendor ID and product ID registers
>
> I think this patch should be reverted until a better solution is found.
> After all, at this point it is effectively unknown if there are other
> users (besides devicetree) depending on ulpi_read_id() returning 0 if
> the communication with the device fails.

I don't see how any code could rely on not having DT and a timeout while 
attempting to enumerate and still expecting success (0). dwc3 in that 
case just assumes ulpi found and continues probe leading to 
non-functional dwc3 host.
I think a fix should be relatively simple to find and resolve 2 bads.

> Guenter