linux-kernel - Re: [PATCH 06/20] drm/msm: Use iommu_paging_domain

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Date: Thu, 30 May 2024 09:57:44 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Jason Gunthorpe <jgg@...pe.ca>, Kevin Tian <kevin.tian@...el.com>,
 Yi Liu <yi.l.liu@...el.com>, David Airlie <airlied@...il.com>,
 Daniel Vetter <daniel@...ll.ch>, Kalle Valo <kvalo@...nel.org>,
 Bjorn Andersson <andersson@...nel.org>,
 Mathieu Poirier <mathieu.poirier@...aro.org>,
 Alex Williamson <alex.williamson@...hat.com>, mst@...hat.com,
 Jason Wang <jasowang@...hat.com>, Thierry Reding <thierry.reding@...il.com>,
 Jonathan Hunter <jonathanh@...dia.com>,
 Mikko Perttunen <mperttunen@...dia.com>, iommu@...ts.linux.dev,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 06/20] drm/msm: Use iommu_paging_domain_alloc()

On 5/29/24 4:21 PM, Dmitry Baryshkov wrote:
> On Wed, May 29, 2024 at 01:32:36PM +0800, Lu Baolu wrote:
>> The domain allocated in msm_iommu_new() is for the @dev. Replace
>> iommu_domain_alloc() with iommu_paging_domain_alloc() to make it explicit.
>>
>> Update msm_iommu_new() to always return ERR_PTR in failure cases instead
>> of NULL.
> Please don't mix unrelated changes, because ...
> 
>> Signed-off-by: Lu Baolu<baolu.lu@...ux.intel.com>
>> ---
>>   drivers/gpu/drm/msm/msm_iommu.c | 8 ++++----
>>   1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/msm/msm_iommu.c b/drivers/gpu/drm/msm/msm_iommu.c
>> index d5512037c38b..f7e28d4b5f62 100644
>> --- a/drivers/gpu/drm/msm/msm_iommu.c
>> +++ b/drivers/gpu/drm/msm/msm_iommu.c
>> @@ -407,9 +407,9 @@ struct msm_mmu *msm_iommu_new(struct device *dev, unsigned long quirks)
>>   	struct msm_iommu *iommu;
>>   	int ret;
>>   
>> -	domain = iommu_domain_alloc(dev->bus);
>> -	if (!domain)
>> -		return NULL;
>> +	domain = iommu_paging_domain_alloc(dev);
>> +	if (IS_ERR(domain))
>> +		return ERR_CAST(domain);
>>   
>>   	iommu_set_pgtable_quirks(domain, quirks);
>>   
>> @@ -441,7 +441,7 @@ struct msm_mmu *msm_iommu_gpu_new(struct device *dev, struct msm_gpu *gpu, unsig
>>   	struct msm_mmu *mmu;
>>   
>>   	mmu = msm_iommu_new(dev, quirks);
>> -	if (IS_ERR_OR_NULL(mmu))
>> +	if (IS_ERR(mmu))
>>   		return mmu;
> NAK, not having an IOMMU is a poor but legit usecase for some of devices
> which don't have IOMMU support yet (for example because of the buggy
> implementation for which we were not able to get all the hooks in).
> 
> Please don't break compatibility for existing platforms.

Sure. I will remove this line of change. Though I have no idea in which
case msm_iommu_new() could return NULL after this patch.

Best regards,
baolu