Re: [PATCH] usb: mtk-xhci: Set the XHCI_NO_64BIT_SUPPORT quirk

From: Nicolas Boichat <drinkcat@chromium.org>
To: Tomasz Figa <tfiga@chromium.org>
Cc: linux-usb@vger.kernel.org,
	Mathias Nyman <mathias.nyman@intel.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	"moderated list:ARM/Mediatek SoC support" 
	<linux-arm-kernel@lists.infradead.org>,
	"moderated list:ARM/Mediatek SoC support" 
	<linux-mediatek@lists.infradead.org>,
	open list <linux-kernel@vger.kernel.org>,
	Chunfeng Yun <chunfeng.yun@mediatek.com>,
	Changqi Hu <Changqi.Hu@mediatek.com>,
	Shik Chen <shik@chromium.org>
Subject: Re: [PATCH] usb: mtk-xhci: Set the XHCI_NO_64BIT_SUPPORT quirk
Date: Thu, 10 Oct 2019 17:37:34 +0800	[thread overview]
Message-ID: <CANMq1KA7pKqJDhFvkuBfEWtr81NUhyRpUE9ZZeTNCCc5Fphoyw@mail.gmail.com> (raw)
In-Reply-To: <CAAFQd5DazVnFGmNENnxT_FHed2Jx30hLT29HyEjxY7xeqLnGCg@mail.gmail.com>

On Thu, Oct 10, 2019 at 5:11 PM Tomasz Figa <tfiga@chromium.org> wrote:
>
> On Thu, Oct 10, 2019 at 6:08 PM Nicolas Boichat <drinkcat@chromium.org> wrote:
> >
> > On Thu, Oct 10, 2019 at 3:50 PM Tomasz Figa <tfiga@chromium.org> wrote:
> > >
> > > MediaTek XHCI host controller does not support 64-bit addressing despite
> > > the AC64 bit of HCCPARAMS1 register being set. The platform-specific
> > > glue sets the DMA mask to 32 bits on its own, but it has no effect,
> > > because xhci_gen_setup() overrides it according to hardware
> > > capabilities.
> > >
> > > Use the XHCI_NO_64BIT_SUPPORT quirk to tell the XHCI core to force
> > > 32-bit DMA mask instead.
> > >
> > > Signed-off-by: Tomasz Figa <tfiga@chromium.org>
> >
> > Can we add a Fixes: tag for stable backports?
> > (after addressing the other comments of course)
> >
>
> The problem with Fixes: is that this patch depends on the quirk being
> there, but the offending code was merged earlier. Do you know how to
> handle such cases?

Oh, interesting. I think this is documented here:
https://github.com/torvalds/linux/blob/master/Documentation/process/stable-kernel-rules.rst

Something like this:
Cc: <stable@vger.kernel.org> # 3.3.x: a1f84a3: sched: Check for idle
Cc: <stable@vger.kernel.org> # 3.3.x

(Where 3.3.x is the first release that contains the commit indicated
in the Fixes tag)

Try that, worst case you'll get automated emails from stable
maintainers asking you how to fix the issue.

>
> >
> > > ---
> > >  drivers/usb/host/xhci-mtk.c | 10 +++++-----
> > >  1 file changed, 5 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/usb/host/xhci-mtk.c b/drivers/usb/host/xhci-mtk.c
> > > index b18a6baef204a..4d101d52cc11b 100644
> > > --- a/drivers/usb/host/xhci-mtk.c
> > > +++ b/drivers/usb/host/xhci-mtk.c
> > > @@ -395,6 +395,11 @@ static void xhci_mtk_quirks(struct device *dev, struct xhci_hcd *xhci)
> > >         xhci->quirks |= XHCI_SPURIOUS_SUCCESS;
> > >         if (mtk->lpm_support)
> > >                 xhci->quirks |= XHCI_LPM_SUPPORT;
> > > +       /*
> > > +        * MTK host controller does not support 64-bit addressing, despite
> > > +        * having the AC64 bit of the HCCPARAMS1 register set.
> > > +        */
> > > +       xhci->quirks |= XHCI_NO_64BIT_SUPPORT;
> > >  }
> > >
> > >  /* called during probe() after chip reset completes */
> > > @@ -488,11 +493,6 @@ static int xhci_mtk_probe(struct platform_device *pdev)
> > >                 goto disable_clk;
> > >         }
> > >
> > > -       /* Initialize dma_mask and coherent_dma_mask to 32-bits */
> > > -       ret = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32));
> > > -       if (ret)
> > > -               goto disable_clk;
> > > -
> > >         hcd = usb_create_hcd(driver, dev, dev_name(dev));
> > >         if (!hcd) {
> > >                 ret = -ENOMEM;
> > > --
> > > 2.23.0.581.g78d2f28ef7-goog
> > >