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From:   Chen-Yu Tsai <wens@csie.org>
Date:   Wed, 31 Jan 2018 11:24:56 +0800
Message-ID: <CAGb2v65T559qcBRnx-e-qbDRkp6TqKvV1JD+pd2r0oGdDYVwUg@mail.gmail.com>
Subject: Re: [linux-sunxi] Re: [PATCH v6 2/2] media: V3s: Add support for
 Allwinner CSI.
To:     Liviu Dudau <liviu@dudau.co.uk>
Cc:     Yong <yong.deng@magewell.com>, kbuild test robot <lkp@intel.com>,
        kbuild-all@01.org,
        Maxime Ripard <maxime.ripard@free-electrons.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
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        Arnd Bergmann <arnd@arndb.de>,
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        Sakari Ailus <sakari.ailus@linux.intel.com>,
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On Wed, Jan 31, 2018 at 11:08 AM, Liviu Dudau <liviu@dudau.co.uk> wrote:
> On Fri, Jan 26, 2018 at 11:00:41AM +0800, Yong wrote:
>> Hi Maxime,
>>
>> On Fri, 26 Jan 2018 09:46:58 +0800
>> Yong <yong.deng@magewell.com> wrote:
>>
>> > Hi Maxime,
>> >
>> > Do you have any experience in solving this problem?
>> > It seems the PHYS_OFFSET maybe undeclared when the ARCH is not arm.
>>
>> Got it.
>> Should I add 'depends on ARM' in Kconfig?
>
> No, I don't think you should do that, you should fix the code.
>
> The dma_addr_t addr that you've got is ideally coming from dma_alloc_coherent(),
> in which case the addr is already "suitable" for use by the device (because the
> bus where the device is attached to does all the address translations). If you
> apply PHYS_OFFSET forcefully to it you might get unexpected results.

As explained in the thread, the dma_addr_t address is based on the kernel
and processor's viewpoint, which has DRAM at an offset. This particular
peripheral (and some others, such as display and video decoder) on Allwinner
platforms do DMA on the separate memory bus directly, which does _not_
have that memory offset. This is specific to our hardware. And also mentioned
is that there is no sensible representation in the device tree that would
allow the DMA API to do proper address translation.

Just throwing it out there, maybe we could do a dummy IOMMU that does the
simple translation of (addr - PHYS_OFFSET)? Still I'm not sure if the device
tree representation would be sane.

ChenYu

>>
>> >
>> > On Fri, 26 Jan 2018 08:04:18 +0800
>> > kbuild test robot <lkp@intel.com> wrote:
>> >
>> > > Hi Yong,
>> > >
>> > > I love your patch! Yet something to improve:
>> > >
>> > > [auto build test ERROR on linuxtv-media/master]
>> > > [also build test ERROR on v4.15-rc9 next-20180119]
>> > > [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
>> > >
>> > > url:    https://github.com/0day-ci/linux/commits/Yong-Deng/dt-bindings-media-Add-Allwinner-V3s-Camera-Sensor-Interface-CSI/20180126-054511
>> > > base:   git://linuxtv.org/media_tree.git master
>> > > config: i386-allmodconfig (attached as .config)
>> > > compiler: gcc-7 (Debian 7.2.0-12) 7.2.1 20171025
>> > > reproduce:
>> > >         # save the attached .config to linux build tree
>> > >         make ARCH=i386
>> > >
>> > > All errors (new ones prefixed by >>):
>> > >
>> > >    drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c: In function 'sun6i_csi_update_buf_addr':
>> > > >> drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c:567:31: error: 'PHYS_OFFSET' undeclared (first use in this function); did you mean 'PAGE_OFFSET'?
>> > >      dma_addr_t bus_addr = addr - PHYS_OFFSET;
>> > >                                   ^~~~~~~~~~~
>> > >                                   PAGE_OFFSET
>> > >    drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c:567:31: note: each undeclared identifier is reported only once for each function it appears in
>> > >
>> > > vim +567 drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c
>> > >
>> > >    562
>> > >    563    void sun6i_csi_update_buf_addr(struct sun6i_csi *csi, dma_addr_t addr)
>> > >    564    {
>> > >    565            struct sun6i_csi_dev *sdev = sun6i_csi_to_dev(csi);
>> > >    566            /* transform physical address to bus address */
>> > >  > 567            dma_addr_t bus_addr = addr - PHYS_OFFSET;
>> > >    568
>> > >    569            regmap_write(sdev->regmap, CSI_CH_F0_BUFA_REG,
>> > >    570                         (bus_addr + sdev->planar_offset[0]) >> 2);
>> > >    571            if (sdev->planar_offset[1] != -1)
>> > >    572                    regmap_write(sdev->regmap, CSI_CH_F1_BUFA_REG,
>> > >    573                                 (bus_addr + sdev->planar_offset[1]) >> 2);
>> > >    574            if (sdev->planar_offset[2] != -1)
>> > >    575                    regmap_write(sdev->regmap, CSI_CH_F2_BUFA_REG,
>> > >    576                                 (bus_addr + sdev->planar_offset[2]) >> 2);
>> > >    577    }
>> > >    578
>> > >
>> > > ---
>> > > 0-DAY kernel test infrastructure                Open Source Technology Center
>> > > https://lists.01.org/pipermail/kbuild-all                   Intel Corporation
>> >
>> >
>> > Thanks,
>> > Yong
>>
>>
>> Thanks,
>> Yong
>>
>> --
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