Re: [PATCH] drm/panthor: Fix firmware initialization on systems with a page size > 4k

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

On Fri, 11 Oct 2024 18:58:45 +0100
Adrián Larumbe <adrian.larumbe@collabora.com> wrote:

> Hi Boris,
> 
> On 09.10.2024 09:10, Steven Price wrote:
> > On 08/10/2024 09:47, Boris Brezillon wrote:  
> > > The system and GPU MMU page size might differ, which becomes a
> > > problem for FW sections that need to be mapped at explicit address
> > > since our PAGE_SIZE alignment might cover a VA range that's
> > > expected to be used for another section.
> > > 
> > > Make sure we never map more than we need.
> > > 
> > > Fixes: 2718d91816ee ("drm/panthor: Add the FW logical block")
> > > Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>  
> > 
> > Reviewed-by: Steven Price <steven.price@arm.com>
> >   
> > > ---
> > >  drivers/gpu/drm/panthor/panthor_fw.c  |  3 +--
> > >  drivers/gpu/drm/panthor/panthor_gem.c | 11 ++++++++---
> > >  drivers/gpu/drm/panthor/panthor_mmu.c |  6 +++---
> > >  3 files changed, 12 insertions(+), 8 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/panthor/panthor_fw.c b/drivers/gpu/drm/panthor/panthor_fw.c
> > > index ef232c0c2049..293846400296 100644
> > > --- a/drivers/gpu/drm/panthor/panthor_fw.c
> > > +++ b/drivers/gpu/drm/panthor/panthor_fw.c
> > > @@ -515,8 +515,7 @@ static int panthor_fw_load_section_entry(struct panthor_device *ptdev,
> > >  		return -EINVAL;
> > >  	}
> > >  
> > > -	if ((hdr.va.start & ~PAGE_MASK) != 0 ||
> > > -	    (hdr.va.end & ~PAGE_MASK) != 0) {
> > > +	if (!IS_ALIGNED(hdr.va.start, SZ_4K) || !IS_ALIGNED(hdr.va.end, SZ_4K)) {
> > >  		drm_err(&ptdev->base, "Firmware corrupted, virtual addresses not page aligned: 0x%x-0x%x\n",
> > >  			hdr.va.start, hdr.va.end);
> > >  		return -EINVAL;
> > > diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
> > > index c60b599665d8..2c8d6e2c7232 100644
> > > --- a/drivers/gpu/drm/panthor/panthor_gem.c
> > > +++ b/drivers/gpu/drm/panthor/panthor_gem.c
> > > @@ -44,8 +44,7 @@ void panthor_kernel_bo_destroy(struct panthor_kernel_bo *bo)
> > >  			to_panthor_bo(bo->obj)->exclusive_vm_root_gem != panthor_vm_root_gem(vm)))
> > >  		goto out_free_bo;
> > >  
> > > -	ret = panthor_vm_unmap_range(vm, bo->va_node.start,
> > > -				     panthor_kernel_bo_size(bo));
> > > +	ret = panthor_vm_unmap_range(vm, bo->va_node.start, bo->va_node.size);
> > >  	if (ret)
> > >  		goto out_free_bo;
> > >  
> > > @@ -95,10 +94,16 @@ panthor_kernel_bo_create(struct panthor_device *ptdev, struct panthor_vm *vm,
> > >  	}
> > >  	bo = to_panthor_bo(&obj->base);
> > > -	size = obj->base.size;
> > >  	kbo->obj = &obj->base;
> > >  	bo->flags = bo_flags;
> > >  
> > > +	/* The system and GPU MMU page size might differ, which becomes a
> > > +	 * problem for FW sections that need to be mapped at explicit address
> > > +	 * since our PAGE_SIZE alignment might cover a VA range that's
> > > +	 * expected to be used for another section.
> > > +	 * Make sure we never map more than we need.
> > > +	 */  
> 
> I was wondering, this must be a relatively common situation for other DRM
> drivers, so maybe the DRM shmem core should have a BO creation function that
> lets you specify an exact page alignment?

So, there's a difference between the MMU page granularity and the system
page size. The BO allocation granularity will always be the system page
size, because gem_shmem can't allocate partial pages.

> 
> > > +	size = ALIGN(size, SZ_4K);  
> 
> I was thinking, if we know that the FW's page size is always 4KiB, maybe we could do
> 
> #define CSF_FW_PAGESIZE SZ_4K
> 
> somewhere in panthor_fw.h to make things clearer?

That I can do. If we want it to be fully dynamic, we can even make it a
panthor_mmu_get_page_size() helper which queries the pgsize_bitmap of
the io_pgtable to get the minimum granularity.