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 17:09:54 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Yuehaibing <yuehaibing@...wei.com>,
        Robin Murphy <robin.murphy@....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 17:03, 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.