[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v2 4/8] xen/arm: Remove support for MSI on SMMUv3
Hi Rahul, On 02/12/2020 13:12, Rahul Singh wrote: Hello Stefano,On 2 Dec 2020, at 12:40 am, Stefano Stabellini <sstabellini@xxxxxxxxxx> wrote: On Tue, 1 Dec 2020, Stefano Stabellini wrote:On Thu, 26 Nov 2020, Rahul Singh wrote:XEN does not support MSI on ARM platforms, therefore remove the MSI support from SMMUv3 driver. Signed-off-by: Rahul Singh <rahul.singh@xxxxxxx>I wonder if it makes sense to #ifdef CONFIG_MSI this code instead of removing it completely.One more thought: could this patch be achieved by reverting 166bdbd23161160f2abcea70621adba179050bee ? If this patch could be done by a couple of revert, it would be great to say it in the commit message.Ok will add in next version.In the past, we tried to keep the entire file as textually similar to the original Linux driver as possible to make it easier to backport features and fixes. So, in this case we would probably not even used an #ifdef but maybe something like: if (/* msi_enabled */ 0) return; at the beginning of arm_smmu_setup_msis. However, that strategy didn't actually work very well because backports have proven difficult to do anyway. So at that point we might as well at least have clean code in Xen and do the changes properly. It was difficult because Linux decided to rework how IOMMU drivers works. I agree the risk is still there and therefore clean code would be better with some caveats (see below). Main reason to remove the feature/code that is not usable in XEN is to have a clean code. I agree that short term this feature will not be usable. However, I think we need to think about {medium, long}-term plan to avoid extra effort in the future because the driver evolve in a way making the revert of revert impossible. Therefore I would prefer to keep both the MSI and PCI ATS present as they are going to be useful/necessary on some platforms. It doesn't matter that they don't work because the driver will be in tech preview. Cheers, -- Julien Grall
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