linux-kernel - Re: [PATCH] usb/host/pci-quirks: Only reset USB bus on NVIDIA devices

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Date:   Mon, 2 Jul 2018 11:45:26 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Paul Menzel <pmenzel@...gen.mpg.de>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <stable@...r.kernel.org>
Subject: Re: [PATCH] usb/host/pci-quirks: Only reset USB bus on NVIDIA devices

On Sun, 1 Jul 2018, Paul Menzel wrote:

> Currently, on the AMD board Asus F2A85-M Pro there is a 100 ms delay as
> the USB bus of each of the two OHCI PCI devices is reset. As a 50 ms
> delay is done per the USB specification.
> 
> Commit c6187597 (OHCI: final fix for NVIDIA problems (I hope))
> unconditionally does the bus reset for
>  all chipsets, while it was only doen for NVIDIA chipsets before.

I don't follow this at all.  Prior to that commit, the bus reset (i.e.,

	writel(control & OHCI_CTRL_MASK, base + OHCI_CONTROL);

) was performed unconditionally for _all_ controllers.  (However, the
50-ms delay was used only for NVIDIA hardware.)  Following that commit,
the reset is performed for all controllers, but only if the HCFS
bitfield is nonzero.

> As it should not be needed for non-NVIDIA chipsets, only do the reset
> for Nvidia devices.

Therefore this reasoning is wrong.

> Tested on Asus F2A85-M PRO and ASRock E350M1. The USB keyboard works and
> the LUKS passphrase can be e
> ntered.

Unfortunately, there is a wide variety of OHCI controller hardware 
available.  Something that works on one or two controllers might not 
work on another.

Besides, doesn't it seem like a bad idea to reset the controller while 
leaving devices on the USB bus in whatever state they happened to be?

Alan Stern

> Signed-off-by: Paul Menzel <pmenzel@...gen.mpg.de>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: linux-usb@...r.kernel.org
> Cc: Alan Stern <stern@...land.harvard.edu>
> Cc: linux-kernel@...r.kernel.org
> Cc: stable@...r.kernel.org
> ---
>  drivers/usb/host/pci-quirks.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/host/pci-quirks.c b/drivers/usb/host/pci-quirks.c
> index 3625a5c1a41b..f6b1a9bbe301 100644
> --- a/drivers/usb/host/pci-quirks.c
> +++ b/drivers/usb/host/pci-quirks.c
> @@ -784,7 +784,7 @@ static void quirk_usb_handoff_ohci(struct pci_dev *pdev)
>  	writel((u32) ~0, base + OHCI_INTRDISABLE);
>  
>  	/* Reset the USB bus, if the controller isn't already in RESET */
> -	if (control & OHCI_HCFS) {
> +	if ((pdev->vendor == PCI_VENDOR_ID_NVIDIA) && (control & OHCI_HCFS)) {
>  		/* Go into RESET, preserving RWC (and possibly IR) */
>  		writel(control & OHCI_CTRL_MASK, base + OHCI_CONTROL);
>  		readl(base + OHCI_CONTROL);
>