Re: [PATCH v2] drm/panthor: flush FW AS caches in slow reset path

[Boris Brezillon <boris.brezillon@collabora.com>]

On Mon, 2 Sep 2024 16:11:51 +0100
Steven Price <steven.price@arm.com> wrote:

> On 02/09/2024 14:02, Adrián Larumbe wrote:
> > In the off-chance that waiting for the firmware to signal its booted status
> > timed out in the fast reset path, one must flush the cache lines for the
> > entire FW VM address space before reloading the regions, otherwise stale
> > values eventually lead to a scheduler job timeout.
> > 
> > Fixes: 647810ec2476 ("drm/panthor: Add the MMU/VM logical block")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
> > Acked-by: Liviu Dudau <liviu.dudau@arm.com>  
> 
> Reviewed-by: Steven Price <steven.price@arm.com>

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

> 
> > ---
> >  drivers/gpu/drm/panthor/panthor_fw.c  |  8 +++++++-
> >  drivers/gpu/drm/panthor/panthor_mmu.c | 21 ++++++++++++++++++---
> >  drivers/gpu/drm/panthor/panthor_mmu.h |  1 +
> >  3 files changed, 26 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/panthor/panthor_fw.c b/drivers/gpu/drm/panthor/panthor_fw.c
> > index 857f3f11258a..ef232c0c2049 100644
> > --- a/drivers/gpu/drm/panthor/panthor_fw.c
> > +++ b/drivers/gpu/drm/panthor/panthor_fw.c
> > @@ -1089,6 +1089,12 @@ int panthor_fw_post_reset(struct panthor_device *ptdev)
> >  		panthor_fw_stop(ptdev);
> >  		ptdev->fw->fast_reset = false;
> >  		drm_err(&ptdev->base, "FW fast reset failed, trying a slow reset");
> > +
> > +		ret = panthor_vm_flush_all(ptdev->fw->vm);
> > +		if (ret) {
> > +			drm_err(&ptdev->base, "FW slow reset failed (couldn't flush FW's AS l2cache)");
> > +			return ret;
> > +		}
> >  	}
> >  
> >  	/* Reload all sections, including RO ones. We're not supposed
> > @@ -1099,7 +1105,7 @@ int panthor_fw_post_reset(struct panthor_device *ptdev)
> >  
> >  	ret = panthor_fw_start(ptdev);
> >  	if (ret) {
> > -		drm_err(&ptdev->base, "FW slow reset failed");
> > +		drm_err(&ptdev->base, "FW slow reset failed (couldn't start the FW )");
> >  		return ret;
> >  	}
> >  
> > diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
> > index d47972806d50..bbc12728437f 100644
> > --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> > +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> > @@ -576,6 +576,12 @@ static int mmu_hw_do_operation_locked(struct panthor_device *ptdev, int as_nr,
> >  	if (as_nr < 0)
> >  		return 0;
> >  
> > +	/*
> > +	 * If the AS number is greater than zero, then we can be sure
> > +	 * the device is up and running, so we don't need to explicitly
> > +	 * power it up
> > +	 */
> > +
> >  	if (op != AS_COMMAND_UNLOCK)
> >  		lock_region(ptdev, as_nr, iova, size);
> >  
> > @@ -874,14 +880,23 @@ static int panthor_vm_flush_range(struct panthor_vm *vm, u64 iova, u64 size)
> >  	if (!drm_dev_enter(&ptdev->base, &cookie))
> >  		return 0;
> >  
> > -	/* Flush the PTs only if we're already awake */
> > -	if (pm_runtime_active(ptdev->base.dev))
> > -		ret = mmu_hw_do_operation(vm, iova, size, AS_COMMAND_FLUSH_PT);
> > +	ret = mmu_hw_do_operation(vm, iova, size, AS_COMMAND_FLUSH_PT);
> >  
> >  	drm_dev_exit(cookie);
> >  	return ret;
> >  }
> >  
> > +/**
> > + * panthor_vm_flush_all() - Flush L2 caches for the entirety of a VM's AS
> > + * @vm: VM whose cache to flush
> > + *
> > + * Return: 0 on success, a negative error code if flush failed.
> > + */
> > +int panthor_vm_flush_all(struct panthor_vm *vm)
> > +{
> > +	return panthor_vm_flush_range(vm, vm->base.mm_start, vm->base.mm_range);
> > +}
> > +
> >  static int panthor_vm_unmap_pages(struct panthor_vm *vm, u64 iova, u64 size)
> >  {
> >  	struct panthor_device *ptdev = vm->ptdev;
> > diff --git a/drivers/gpu/drm/panthor/panthor_mmu.h b/drivers/gpu/drm/panthor/panthor_mmu.h
> > index f3c1ed19f973..6788771071e3 100644
> > --- a/drivers/gpu/drm/panthor/panthor_mmu.h
> > +++ b/drivers/gpu/drm/panthor/panthor_mmu.h
> > @@ -31,6 +31,7 @@ panthor_vm_get_bo_for_va(struct panthor_vm *vm, u64 va, u64 *bo_offset);
> >  int panthor_vm_active(struct panthor_vm *vm);
> >  void panthor_vm_idle(struct panthor_vm *vm);
> >  int panthor_vm_as(struct panthor_vm *vm);
> > +int panthor_vm_flush_all(struct panthor_vm *vm);
> >  
> >  struct panthor_heap_pool *
> >  panthor_vm_get_heap_pool(struct panthor_vm *vm, bool create);  
>