linux-kernel - Re: [PATCH] usb: xhci: Error enumerating USB TV Tuner

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Message-ID: <74c294a3-8eaa-a48e-3371-a7027d5aabd2@linux.intel.com>
Date:   Mon, 9 Mar 2020 14:22:17 +0200
From:   Mathias Nyman <mathias.nyman@...ux.intel.com>
To:     Al Cooper <alcooperx@...il.com>, linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, Mathias Nyman <mathias.nyman@...el.com>
Subject: Re: [PATCH] usb: xhci: Error enumerating USB TV Tuner

On 6.3.2020 18.06, Al Cooper wrote:
> Unable to complete the enumeration of a USB TV Tuner device.
> 
> Per XHCI spec (4.6.5), the EP state field of the input context shall
> be cleared for a set address command. In the special case of an FS
> device that has "MaxPacketSize0 = 8", the Linux XHCI driver does
> not do this before evaluating the context. With an XHCI controller
> that checks the EP state field for parameter context error this
> causes a problem in cases such as the device getting reset again
> after enumeration.
> 
> When that field is cleared, the problem does not occur.
> 
> This was found and fixed by Sasi Kumar.
> 
> Signed-off-by: Al Cooper <alcooperx@...il.com>
> ---
>  drivers/usb/host/xhci.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
> index dbac0fa9748d..5f034e143082 100644
> --- a/drivers/usb/host/xhci.c
> +++ b/drivers/usb/host/xhci.c
> @@ -1428,6 +1428,7 @@ static int xhci_check_maxpacket(struct xhci_hcd *xhci, unsigned int slot_id,
>  				xhci->devs[slot_id]->out_ctx, ep_index);
>  
>  		ep_ctx = xhci_get_ep_ctx(xhci, command->in_ctx, ep_index);
> +		ep_ctx->ep_info &= cpu_to_le32(~EP_STATE_MASK);/* must clear */
>  		ep_ctx->ep_info2 &= cpu_to_le32(~MAX_PACKET_MASK);
>  		ep_ctx->ep_info2 |= cpu_to_le32(MAX_PACKET(max_packet_size));
>  
> 

Thanks, nice catch.

If you agree I'd like to change the the subject of this patch to something like:
"xhci: Fix enumeration issue when setting actual max packet size for FS devices"

While looking at this it seems that the current EP_STATE_MASK is not correct either.
It should be 0x7 instead of 0xf.

-Mathias