On Thu, Jun 04, 2020 at 10:11:18AM +0800, Longfang Liu wrote:
> A Synopsys USB2.0 core used in Huawei Kunpeng920 SoC has a bug which
> might cause the host controller not issuing ping.
>
> Bug description:
> After indicating an Interrupt on Async Advance, the software uses the
> doorbell mechanism to delete the Next Link queue head of the last
> executed queue head. At this time, the host controller still references
> the removed queue head(the queue head is NULL). NULL reference causes
> the host controller to lose the USB device.
>
> Solution:
> After deleting the Next Link queue head, the software can write one of the
> valid queue head addresses to the ASYNCLISTADDR register to allow
> the host controller to get the valid queue head.
>
> There are detailed instructions and solutions in this patch:
> commit 2f7ac6c19997 ("USB: ehci: add workaround for Synopsys HC bug")
>
> Signed-off-by: Longfang Liu <liulongfang@xxxxxxxxxx>
This is a very bad patch description. Do you understand why? Because
it doesn't describe what the patch actually does!
The description talks about the original bug -- what it was and how it
was fixed. But this patch doesn't contain the bug fix. Instead, all
this patch does is set a quirk flag for the Huawei Kunpeng920. The
patch description should explain why the quirk flag needs to be set; it
doesn't have to explain the original bug.
Alan Stern
> ---
>
> Changes in V2:
> - updated comment message
>
> drivers/usb/host/ehci-pci.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/drivers/usb/host/ehci-pci.c b/drivers/usb/host/ehci-pci.c
> index 1a48ab1..7ff2cbd 100644
> --- a/drivers/usb/host/ehci-pci.c
> +++ b/drivers/usb/host/ehci-pci.c
> @@ -216,6 +216,13 @@ static int ehci_pci_setup(struct usb_hcd *hcd)
> ehci_info(ehci, "applying MosChip frame-index workaround\n");
> ehci->frame_index_bug = 1;
> break;
> + case PCI_VENDOR_ID_HUAWEI:
> + /* Synopsys HC bug */
> + if (pdev->device == 0xa239) {
> + ehci_info(ehci, "applying Synopsys HC workaround\n");
> + ehci->has_synopsys_hc_bug = 1;
> + }
> + break;
> }
>
> /* optional debug port, normally in the first BAR */
> --
> 2.8.1
>
