Re: [RESEND PATCH] xhci: Fix Renesas PCIe controllers passthrough issue

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Oct 20, 2022 at 06:39:14PM +0800, wangwenmei168@163.com wrote:
> From: gehao <gehao@kylinos.cn>

This does not match your from: line in the email at all, so we can't
take this :(

Please work with your company's email system to make it possible to send
kernel patches if you wish to be able to contribute.

> 
> When we use uPD720201 USB 3.0 Host Controller passthrough to VM
> guest os will report follow errors and it can not working.
> 
> xhci_hcd 0000:09:00.0: Host took too long to start, waited 16000
> microseconds.
> xhci_hcd 0000:09:00.0: startup error -19.
> 
> Because when we passthroug some device to our guest os,
> dev->iommu_group =NULL,so it will return from this function,
> Actually it still control by host os.
> I think that this condition is not necessary.
> 
> For host os with IOMMU,it is safe.
> For host os with noiommu,doing anything when there is no
> iommu is definitely.
> For guest os,the addresses we can access are restricted.
> 
> After add this path,they all work well.

This line isn't needed in a changelog, right?

> 
> Signed-off-by: gehao <gehao@kylinos.cn>
> ---
>  drivers/usb/host/xhci.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
> index 5176765c4013..e8f4c4ee3ea3 100644
> --- a/drivers/usb/host/xhci.c
> +++ b/drivers/usb/host/xhci.c
> @@ -241,12 +241,8 @@ static void xhci_zero_64b_regs(struct xhci_hcd *xhci)
>  	 * changing the programming leads to extra accesses even if the
>  	 * controller is supposed to be halted. The controller ends up with
>  	 * a fatal fault, and is then ripe for being properly reset.
> -	 *
> -	 * Special care is taken to only apply this if the device is behind
> -	 * an iommu. Doing anything when there is no iommu is definitely
> -	 * unsafe...

How many different systems did you test this on to verify that this is
now ok to do?

thanks,

greg k-h