Messages in this thread | | | Date | Wed, 21 Dec 2022 19:38:52 +0100 | Subject | Re: [PATCH v5 1/2] usb: ulpi: defer ulpi_register on ulpi_read_id timeout | From | Ferry Toth <> |
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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@vger.kernel.org >>>>>> Signed-off-by: Ferry Toth <ftoth@exalondelft.nl> >>>>> 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
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