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

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Date:   Wed, 24 Jul 2019 15:23:55 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Dmitry Osipenko <digetx@...il.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

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.

Robin.