linux-kernel - Re: [PATCH] iommu/rockchip: Add missing set_platform_dma

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Message-ID: <ZBs8k8nki/iqUiwE@ziepe.ca>
Date:   Wed, 22 Mar 2023 14:36:19 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Steven Price <steven.price@....com>
Cc:     Heiko Stuebner <heiko@...ech.de>, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>, iommu@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-rockchip@...ts.infradead.org,
        Lu Baolu <baolu.lu@...ux.intel.com>
Subject: Re: [PATCH] iommu/rockchip: Add missing set_platform_dma_ops callback

On Wed, Mar 22, 2023 at 04:04:25PM +0000, Steven Price wrote:
> On 22/03/2023 15:16, Jason Gunthorpe wrote:
> > On Wed, Mar 22, 2023 at 03:08:41PM +0000, Steven Price wrote:
> >> @@ -1035,8 +1055,9 @@ static int rk_iommu_attach_device(struct iommu_domain *domain,
> >>  	if (iommu->domain == domain)
> >>  		return 0;
> >>  
> >> -	if (iommu->domain)
> >> -		rk_iommu_detach_device(iommu->domain, dev);
> >> +	ret = rk_iommu_identity_attach(&rk_identity_domain, dev);
> >> +	if (ret)
> >> +		return ret;
> > 
> >>  
> >>  	iommu->domain = domain;
> >>  
> >> @@ -1049,8 +1070,6 @@ static int rk_iommu_attach_device(struct iommu_domain *domain,
> >>  		return 0;
> >>  
> >>  	ret = rk_iommu_enable(iommu);
> >> -	if (ret)
> >> -		rk_iommu_detach_device(iommu->domain, dev);
> > 
> > I think this still needs error handling, it should put it back to the
> > identity domain and return an error code if it fails to attach to the
> > requested domain.
> 
> What confused me here is that there's already a call to
> rk_iommu_identity_attach() just above. But I can obviously add a...

I don't know this driver at all, but to me it looks like this is
perhaps undoing a partially failed rk_iommu_enable() since it doesn't
seem to enetirely fix itself. Ie it zeros the INT_MASK and DTE_ADDR

Maybe it would be better to put that error cleanup direclty into
enable and just move the iommu->domain assignment to after enable
success.

>        if (ret)
>                rk_iommu_identity_attach(&rk_identity_domain, dev);
> 
> ... in here. But I don't know how to handle an error from
> rk_iommu_identity_attach() at this point. Does it need handling - is a
> WARN_ON sufficient?

WARN_ON should be fine, that is kind of hacky, it would be better to
organize things so there is an identity attach function that cannot
fail, ie pre-assumes all the validation is done alread.y

> 
> > It should also initlaize iommu->domain to the identity domain when the
> > iommu struct is allocated. The iommu->domain should never be
> > NULL. identity domain means the IOMMU is turned off which was
> > previously called "detached".
> 
> I presume you mean in rk_iommu_probe()?

It would be best if it was setup at allocation time so in
rk_iommu_of_xlate() before dev_iommu_priv_set()

Jason