linux-kernel - Re: [PATCH] gpu: host1x: Fix compiler errors

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Date:   Tue, 15 May 2018 23:07:30 +0200
From:   Emil Goode <emil.fsw@...de.io>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Thierry Reding <treding@...dia.com>,
        dri-devel@...ts.freedesktop.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] gpu: host1x: Fix compiler errors

Hello,

On Mon, May 14, 2018 at 10:43:08AM +0200, Thierry Reding wrote:
> On Mon, Mar 26, 2018 at 04:44:14PM +0200, Emil Goode wrote:
> > The compiler is complaining with the following errors:
> > 
> > drivers/gpu/host1x/cdma.c:94:48: error:
> > 	passing argument 3 of ‘dma_alloc_wc’ from incompatible pointer type
> > 	[-Werror=incompatible-pointer-types]
> > 
> > drivers/gpu/host1x/cdma.c:113:48: error:
> > 	passing argument 3 of ‘dma_alloc_wc’ from incompatible pointer type
> > 	[-Werror=incompatible-pointer-types]
> > 
> > The expected pointer type of the third argument to dma_alloc_wc() is
> > dma_addr_t but phys_addr_t is passed. Fix this by adding casts to the
> > expected pointer type.
> > 
> > Signed-off-by: Emil Goode <emil.fsw@...de.io>
> > ---
> >  drivers/gpu/host1x/cdma.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/gpu/host1x/cdma.c b/drivers/gpu/host1x/cdma.c
> > index 28541b280739..5e8b321a751e 100644
> > --- a/drivers/gpu/host1x/cdma.c
> > +++ b/drivers/gpu/host1x/cdma.c
> > @@ -91,8 +91,8 @@ static int host1x_pushbuffer_init(struct push_buffer *pb)
> >  
> >  		size = iova_align(&host1x->iova, size);
> >  
> > -		pb->mapped = dma_alloc_wc(host1x->dev, size, &pb->phys,
> > -					  GFP_KERNEL);
> > +		pb->mapped = dma_alloc_wc(host1x->dev, size,
> > +					  (dma_addr_t *)&pb->phys, GFP_KERNEL);
> >  		if (!pb->mapped)
> >  			return -ENOMEM;
> >  
> > @@ -110,8 +110,8 @@ static int host1x_pushbuffer_init(struct push_buffer *pb)
> >  		if (err)
> >  			goto iommu_free_iova;
> >  	} else {
> > -		pb->mapped = dma_alloc_wc(host1x->dev, size, &pb->phys,
> > -					  GFP_KERNEL);
> > +		pb->mapped = dma_alloc_wc(host1x->dev, size,
> > +					  (dma_addr_t *)&pb->phys, GFP_KERNEL);
> >  		if (!pb->mapped)
> >  			return -ENOMEM;
> >  
> 
> This doesn't seem right. There's no guarantee that phys_addr_t and
> dma_addr_t will be compatible, so the above isn't always correct. Also,
> I don't see a need for pb->phys to ever be phys_addr_t. It's allocated
> through dma_alloc_wc() exclusively, so it should just be dma_addr_t.

I agree that this is a better solution, however when changing pb->phys to dma_addr_t
the type will be wrong when it's passed to iommu_map() as phys_addr_t is expected
but that doesn't cause a compilation error.

> Note that the !pb->phys check in host1x_pushbuffer_destroy() becomes
> technically wrong if pb->phys is dma_addr_t (0 is a perfectly valid
> value for dma_addr_t), so make sure to flip that to !pb->mapped instead.
> pb->mapped and pb->phys are always set in tandem, and checking mapped
> for non-NULL is the right check to test whether the pair is valid or
> not.

Ok I will change this as well.

Best regards,

Emil