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In-Reply-To: <9ec5ba90-150a-c675-d95b-b13e3a4e9e10@arm.com>
From:   Yongqin Liu <yongqin.liu@linaro.org>
Date:   Tue, 30 Aug 2022 23:19:04 +0800
Message-ID: <CAMSo37XmxGn4VJJXwOca=mjHfmgYoh-i4bOs_DpP2LdjaN87wA@mail.gmail.com>
Subject: Re: [PATCH 0/3] More ARM DMA ops cleanup
To:     Robin Murphy <robin.murphy@arm.com>
Cc:     Christoph Hellwig <hch@lst.de>, linux@armlinux.org.uk,
        linux-arm-kernel@lists.infradead.org, m.szyprowski@samsung.com,
        arnd@kernel.org, iommu@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org,
        "Bajjuri, Praneeth" <praneeth@ti.com>,
        Sumit Semwal <sumit.semwal@linaro.org>
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Hi, Robin

Thanks for the kind reply!

On Tue, 30 Aug 2022 at 17:48, Robin Murphy <robin.murphy@arm.com> wrote:
>
> On 2022-08-27 13:24, Yongqin Liu wrote:
> > Hi, Robin, Christoph
> >
> > With the changes landed in the mainline kernel,
> > one problem is exposed with our out of tree pvr module.
> > Like the source here[1], arm_dma_ops.sync_single_for_cpu is called in
> > the format like the following:
> >      arm_dma_ops.sync_single_for_cpu(NULL, pStart, pEnd - pStart,
> > DMA_FROM_DEVICE);
> >
> > Not sure if you could give some suggestions on what I should do next
> > to make the pvr module work again.
>
> Wow, that driver reinvents so many standard APIs for no apparent reason
> it's not even funny.
>
> Anyway, from a brief look it seemingly already knows how to call the DMA
> API semi-correctly, so WTF that's doing behind an #ifdef, who knows?
> However it's still so completely wrong in general - fundamentally broken
> AArch64 set/way cache maintenance!? - that it looks largely beyond help.
> "Throw CONFIG_DMA_API_DEBUG at it and cry" is about the extent of
> support I'm prepared to provide for that mess.

For the moment, I do not care about the AArch64 lines, like if we only
say the following two lines:
    arm_dma_ops.sync_single_for_device(NULL, pStart, pEnd - pStart,
DMA_TO_DEVICE);
    arm_dma_ops.sync_single_for_cpu(NULL, pStart, pEnd - pStart,
DMA_FROM_DEVICE);

Could you please give some suggestions for that?

Thanks,
Yongqin Liu


> > Thanks in advance!
> >
> > [1]: https://android-git.linaro.org/kernel/omap-modules.git/tree/pvr/se=
rvices4/srvkm/env/linux/osfunc.c?h=3Dandroid-mainline#n4615
> >
> > Thanks,
> > Yongqin Liu
> >
> > On Thu, 21 Apr 2022 at 22:35, Robin Murphy <robin.murphy@arm.com> wrote=
:
> >>
> >> On 2022-04-21 15:13, Christoph Hellwig wrote:
> >>> On Thu, Apr 21, 2022 at 12:36:56PM +0100, Robin Murphy wrote:
> >>>> Hi all,
> >>>>
> >>>> Thanks to Christoph's latest series, I'm reminded that, if we're goi=
ng
> >>>> to give the ARM DMA ops some cleanup this cycle, it's as good a time=
 as
> >>>> any to dust off these old patches and add them on top as well. I've
> >>>> based these on the arm-dma-direct branch which I assume matches the
> >>>> patches posted at [1].
> >>>
> >>> All these do look sensible to me.  But weren't you working on replaci=
ng
> >>> the ARM iommu dma_ops with dma-=D1=96ommu anyway?
> >>
> >> Yes, that's somewhat entangled with the IOMMU bus ops stuff, so I'll
> >> probably get to the point of having to revisit it in a couple of month=
s
> >> or so. These patches are off the bottom of that stack from my first
> >> attempt, where the aim was to make the current ops the same shape firs=
t
> >> so that the switch is then easier to reason about (particularly in ter=
ms
> >> of sounding out any issues with the hooking up of dev->dma_coherent,
> >> although your series will now be taking most of the load off there).
> >>
> >> Cheers,
> >> Robin.
> >
> >
> >


--=20
Best Regards,
Yongqin Liu
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