linux-kernel - Re: [PATCH] media: staging: ipu3: Enable IOVA API only when IOMMU support is enabled

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Message-ID: <dc354ede-5963-cd7f-ee53-f3df3061d39a@gmail.com>
Date:   Wed, 24 Jul 2019 17:28:49 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Robin Murphy <robin.murphy@....com>,
        Yuehaibing <yuehaibing@...wei.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc:     devel@...verdev.osuosl.org, linux-media@...r.kernel.org,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        iommu@...ts.linux-foundation.org, hverkuil-cisco@...all.nl,
        mchehab@...nel.org, yong.zhi@...el.com
Subject: Re: [PATCH] media: staging: ipu3: Enable IOVA API only when IOMMU
 support is enabled

24.07.2019 17:23, Robin Murphy пишет:
> On 24/07/2019 15:09, Dmitry Osipenko wrote:
>> 24.07.2019 17:03, Yuehaibing пишет:
>>> On 2019/7/24 21:49, Robin Murphy wrote:
>>>> On 24/07/2019 11:30, Sakari Ailus wrote:
>>>>> Hi Yue,
>>>>>
>>>>> On Mon, Jul 22, 2019 at 09:47:49PM +0800, YueHaibing wrote:
>>>>>> If IOMMU_SUPPORT is not set, ipu3 driver may select IOMMU_IOVA to m.
>>>>>> But for many drivers, they use "select IOMMU_IOVA if IOMMU_SUPPORT"
>>>>>> in the Kconfig, for example, CONFIG_TEGRA_VDE is set to y but
>>>>>> IOMMU_IOVA
>>>>>> is m, then the building fails like this:
>>>>>>
>>>>>> drivers/staging/media/tegra-vde/iommu.o: In function
>>>>>> `tegra_vde_iommu_map':
>>>>>> iommu.c:(.text+0x41): undefined reference to `alloc_iova'
>>>>>> iommu.c:(.text+0x56): undefined reference to `__free_iova'
>>>>>>
>>>>>> Reported-by: Hulk Robot <hulkci@...wei.com>
>>>>>> Fixes: 7fc7af649ca7 ("media: staging/intel-ipu3: Add imgu top
>>>>>> level pci device driver")
>>>>>> Signed-off-by: YueHaibing <yuehaibing@...wei.com>
>>>>>> ---
>>>>>>    drivers/staging/media/ipu3/Kconfig | 2 +-
>>>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/drivers/staging/media/ipu3/Kconfig
>>>>>> b/drivers/staging/media/ipu3/Kconfig
>>>>>> index 4b51c67..b7df18f 100644
>>>>>> --- a/drivers/staging/media/ipu3/Kconfig
>>>>>> +++ b/drivers/staging/media/ipu3/Kconfig
>>>>>> @@ -4,7 +4,7 @@ config VIDEO_IPU3_IMGU
>>>>>>        depends on PCI && VIDEO_V4L2
>>>>>>        depends on MEDIA_CONTROLLER && VIDEO_V4L2_SUBDEV_API
>>>>>>        depends on X86
>>>>>> -    select IOMMU_IOVA
>>>>>> +    select IOMMU_IOVA if IOMMU_SUPPORT
>>>>>
>>>>> This doesn't seem right: the ipu3-cio2 driver needs IOMMU_IOVA
>>>>> independently of IOMMU_SUPPORT.
>>>>>
>>>>> Looking at tegra-vde, it seems to depend on IOMMU_SUPPORT but
>>>>> that's not
>>>>> declared in its Kconfig entry. I wonder if adding that would be the
>>>>> right
>>>>> way to fix this.
>>>>>
>>>>> Cc'ing the IOMMU list.
>> IOMMU_SUPPORT is optional for the Tegra-VDE driver.
>>
>>>> Right, I also had the impression that we'd made the IOVA library
>>>> completely standalone. And what does the IPU3 driver's Kconfig have
>>>> to do with some *other* driver failing to link anyway?
>>
>> I can see it failing if IPU3 is compiled as a loadable module, while
>> Tegra-VDE is a built-in driver. Hence IOVA lib should be also a kernel
>> module and thus the IOVA symbols will be missing during of linkage of
>> the VDE driver.
>>
>>> Oh, I misunderstand that IOMMU_IOVA is depend on IOMMU_SUPPORT, thank
>>> you for clarification.
>>>
>>> I will try to fix this in tegra-vde.
>>
>> Probably IOVA could be selected independently of IOMMU_SUPPORT, but IOVA
>> library isn't needed for the VDE driver if IOMMU_SUPPORT is disabled.
> 
> Oh, I think I get the problem now - tegra-vde/iommu.c is built
> unconditionally and relies on the static inline stubs for IOMMU and IOVA
> calls if !IOMMU_SUPPORT, but in a compile-test config where IOVA=m for
> other reasons, it then picks up the real declarations from linux/iova.h
> instead of the stubs, and things go downhill from there. So there is a
> real issue, but indeed it's Tegra-VDE which needs to be restructured to
> cope with such configurations, and not IPU3's (or anyone else who may
> select IOVA=m in future) job to work around it.

I guess it could be:

	select IOMMU_IOVA if (IOMMU_SUPPORT || COMPILE_TEST)

as a workaround.