[PATCH] drm/panthor: Don't use virt_to_pfn()

[Boris Brezillon]

On Mon, 18 Mar 2024 15:11:42 +0000
Robin Murphy <robin.murphy at arm.com> wrote:

> On 18/03/2024 2:51 pm, Steven Price wrote:
> > virt_to_pfn() isn't available on x86 (except to xen) so breaks
> > COMPILE_TEST builds. Avoid its use completely by instead storing the
> > struct page pointer allocated in panthor_device_init() and using
> > page_to_pfn() instead.
> > 
> > Signed-off-by: Steven Price <steven.price at arm.com>
> > ---
> >   drivers/gpu/drm/panthor/panthor_device.c | 10 ++++++----
> >   drivers/gpu/drm/panthor/panthor_device.h |  2 +-
> >   2 files changed, 7 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/panthor/panthor_device.c b/drivers/gpu/drm/panthor/panthor_device.c
> > index 69deb8e17778..3c30da03fa48 100644
> > --- a/drivers/gpu/drm/panthor/panthor_device.c
> > +++ b/drivers/gpu/drm/panthor/panthor_device.c
> > @@ -154,6 +154,7 @@ int panthor_device_init(struct panthor_device *ptdev)
> >   {
> >   	struct resource *res;
> >   	struct page *p;
> > +	u32 *dummy_page_virt;
> >   	int ret;
> >   
> >   	ptdev->coherent = device_get_dma_attr(ptdev->base.dev) == DEV_DMA_COHERENT;
> > @@ -172,9 +173,10 @@ int panthor_device_init(struct panthor_device *ptdev)
> >   	if (!p)
> >   		return -ENOMEM;
> >   
> > -	ptdev->pm.dummy_latest_flush = page_address(p);
> > +	ptdev->pm.dummy_latest_flush = p;
> > +	dummy_page_virt = page_address(p);
> >   	ret = drmm_add_action_or_reset(&ptdev->base, panthor_device_free_page,
> > -				       ptdev->pm.dummy_latest_flush);
> > +				       dummy_page_virt);  
> 
> Nit: I was about to say I'd be inclined to switch the callback to 
> __free_page() instead, but then I realise there's no real need to be 
> reinventing that in the first place:
> 
> 	dummy_page_virt = (void *)devm_get_free_pages(ptdev->base.dev,
> 					GFP_KERNEL | GFP_ZERO, 0);

IIRC, the drm_device object might outlive the device it's been created
from if a process holds on the DRM dev FD after an unplug happened,
which can happen if panthor_device_unplug() is called from the reset
path (when a reset fails).

> 	if (!dummy_page_virt)
> 		return -ENOMEM;
> 
> 	ptdev->pm.dummy_latest_flush = virt_to_page(dummy_page_virt);
> 
> Cheers,
> Robin.
> 
> >   	if (ret)
> >   		return ret;
> >   
> > @@ -184,7 +186,7 @@ int panthor_device_init(struct panthor_device *ptdev)
> >   	 * happens while the dummy page is mapped. Zero cannot be used because
> >   	 * that means 'always flush'.
> >   	 */
> > -	*ptdev->pm.dummy_latest_flush = 1;
> > +	*dummy_page_virt = 1;
> >   
> >   	INIT_WORK(&ptdev->reset.work, panthor_device_reset_work);
> >   	ptdev->reset.wq = alloc_ordered_workqueue("panthor-reset-wq", 0);
> > @@ -353,7 +355,7 @@ static vm_fault_t panthor_mmio_vm_fault(struct vm_fault *vmf)
> >   		if (active)
> >   			pfn = __phys_to_pfn(ptdev->phys_addr + CSF_GPU_LATEST_FLUSH_ID);
> >   		else
> > -			pfn = virt_to_pfn(ptdev->pm.dummy_latest_flush);
> > +			pfn = page_to_pfn(ptdev->pm.dummy_latest_flush);
> >   		break;
> >   
> >   	default:
> > diff --git a/drivers/gpu/drm/panthor/panthor_device.h b/drivers/gpu/drm/panthor/panthor_device.h
> > index 51c9d61b6796..c84c27dcc92c 100644
> > --- a/drivers/gpu/drm/panthor/panthor_device.h
> > +++ b/drivers/gpu/drm/panthor/panthor_device.h
> > @@ -160,7 +160,7 @@ struct panthor_device {
> >   		 * Used to replace the real LATEST_FLUSH page when the GPU
> >   		 * is suspended.
> >   		 */
> > -		u32 *dummy_latest_flush;
> > +		struct page *dummy_latest_flush;
> >   	} pm;
> >   };
> >