linux-kernel - Re: [PATCH] usb: mtk-xhci: Set the XHCI_NO_64BIT

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Date:   Thu, 10 Oct 2019 19:09:06 +0900
From:   Tomasz Figa <tfiga@...omium.org>
To:     Nicolas Boichat <drinkcat@...omium.org>
Cc:     linux-usb@...r.kernel.org, Mathias Nyman <mathias.nyman@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Changqi Hu <Changqi.Hu@...iatek.com>,
        Shik Chen <shik@...omium.org>
Subject: Re: [PATCH] usb: mtk-xhci: Set the XHCI_NO_64BIT_SUPPORT quirk

On Thu, Oct 10, 2019 at 6:37 PM Nicolas Boichat <drinkcat@...omium.org> wrote:
>
> On Thu, Oct 10, 2019 at 5:11 PM Tomasz Figa <tfiga@...omium.org> wrote:
> >
> > On Thu, Oct 10, 2019 at 6:08 PM Nicolas Boichat <drinkcat@...omium.org> wrote:
> > >
> > > On Thu, Oct 10, 2019 at 3:50 PM Tomasz Figa <tfiga@...omium.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@...omium.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@...r.kernel.org> # 3.3.x: a1f84a3: sched: Check for idle
> Cc: <stable@...r.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.
>

Oh, great, thanks a lot!

Best regards,
Tomasz

> >
> > >
> > > > ---
> > > >  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
> > > >