Re: [PATCH v5 08/16] swiotlb: Update is_swiotlb_active to add a struct device argument

[Claire Chang <tientzu@chromium.org>]

On Fri, Apr 23, 2021 at 9:31 PM Robin Murphy <robin.murphy@arm.com> wrote:
>
> On 2021-04-22 09:15, Claire Chang wrote:
> > Update is_swiotlb_active to add a struct device argument. This will be
> > useful later to allow for restricted DMA pool.
> >
> > Signed-off-by: Claire Chang <tientzu@chromium.org>
> > ---
> >   drivers/gpu/drm/i915/gem/i915_gem_internal.c | 2 +-
> >   drivers/gpu/drm/nouveau/nouveau_ttm.c        | 2 +-
> >   drivers/pci/xen-pcifront.c                   | 2 +-
> >   include/linux/swiotlb.h                      | 4 ++--
> >   kernel/dma/direct.c                          | 2 +-
> >   kernel/dma/swiotlb.c                         | 4 ++--
> >   6 files changed, 8 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_internal.c b/drivers/gpu/drm/i915/gem/i915_gem_internal.c
> > index ce6b664b10aa..7d48c433446b 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_internal.c
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_internal.c
> > @@ -42,7 +42,7 @@ static int i915_gem_object_get_pages_internal(struct drm_i915_gem_object *obj)
> >
> >       max_order = MAX_ORDER;
> >   #ifdef CONFIG_SWIOTLB
> > -     if (is_swiotlb_active()) {
> > +     if (is_swiotlb_active(NULL)) {
> >               unsigned int max_segment;
> >
> >               max_segment = swiotlb_max_segment();
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_ttm.c b/drivers/gpu/drm/nouveau/nouveau_ttm.c
> > index e8b506a6685b..2a2ae6d6cf6d 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_ttm.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_ttm.c
> > @@ -321,7 +321,7 @@ nouveau_ttm_init(struct nouveau_drm *drm)
> >       }
> >
> >   #if IS_ENABLED(CONFIG_SWIOTLB) && IS_ENABLED(CONFIG_X86)
> > -     need_swiotlb = is_swiotlb_active();
> > +     need_swiotlb = is_swiotlb_active(NULL);
> >   #endif
> >
> >       ret = ttm_device_init(&drm->ttm.bdev, &nouveau_bo_driver, drm->dev->dev,
> > diff --git a/drivers/pci/xen-pcifront.c b/drivers/pci/xen-pcifront.c
> > index b7a8f3a1921f..6d548ce53ce7 100644
> > --- a/drivers/pci/xen-pcifront.c
> > +++ b/drivers/pci/xen-pcifront.c
> > @@ -693,7 +693,7 @@ static int pcifront_connect_and_init_dma(struct pcifront_device *pdev)
> >
> >       spin_unlock(&pcifront_dev_lock);
> >
> > -     if (!err && !is_swiotlb_active()) {
> > +     if (!err && !is_swiotlb_active(NULL)) {
> >               err = pci_xen_swiotlb_init_late();
> >               if (err)
> >                       dev_err(&pdev->xdev->dev, "Could not setup SWIOTLB!\n");
> > diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> > index 2a6cca07540b..c530c976d18b 100644
> > --- a/include/linux/swiotlb.h
> > +++ b/include/linux/swiotlb.h
> > @@ -123,7 +123,7 @@ static inline bool is_swiotlb_buffer(struct device *dev, phys_addr_t paddr)
> >   void __init swiotlb_exit(void);
> >   unsigned int swiotlb_max_segment(void);
> >   size_t swiotlb_max_mapping_size(struct device *dev);
> > -bool is_swiotlb_active(void);
> > +bool is_swiotlb_active(struct device *dev);
> >   void __init swiotlb_adjust_size(unsigned long size);
> >   #else
> >   #define swiotlb_force SWIOTLB_NO_FORCE
> > @@ -143,7 +143,7 @@ static inline size_t swiotlb_max_mapping_size(struct device *dev)
> >       return SIZE_MAX;
> >   }
> >
> > -static inline bool is_swiotlb_active(void)
> > +static inline bool is_swiotlb_active(struct device *dev)
> >   {
> >       return false;
> >   }
> > diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> > index 84c9feb5474a..7a88c34d0867 100644
> > --- a/kernel/dma/direct.c
> > +++ b/kernel/dma/direct.c
> > @@ -495,7 +495,7 @@ int dma_direct_supported(struct device *dev, u64 mask)
> >   size_t dma_direct_max_mapping_size(struct device *dev)
> >   {
> >       /* If SWIOTLB is active, use its maximum mapping size */
> > -     if (is_swiotlb_active() &&
> > +     if (is_swiotlb_active(dev) &&
> >           (dma_addressing_limited(dev) || swiotlb_force == SWIOTLB_FORCE))
>
> I wonder if it's worth trying to fold these other conditions into
> is_swiotlb_active() itself? I'm not entirely sure what matters for Xen,
> but for the other cases it seems like they probably only care about
> whether bouncing may occur for their particular device or not (possibly
> they want to be using dma_max_mapping_size() now anyway - TBH I'm
> struggling to make sense of what the swiotlb_max_segment business is
> supposed to mean).

I think leaving those conditions outside of is_swiotlb_active() might
help avoid confusion with is_dev_swiotlb_force() in patch #9? We need
is_dev_swiotlb_force() only because the restricted DMA pool supports
memory allocation, but the default swiotlb doesn't.

>
> Otherwise, patch #9 will need to touch here as well to make sure that
> per-device forced bouncing is reflected correctly.

You're right. Otherwise, is_dev_swiotlb_force is needed here.


>
> Robin.
>
> >               return swiotlb_max_mapping_size(dev);
> >       return SIZE_MAX;
> > diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> > index ffbb8724e06c..1d221343f1c8 100644
> > --- a/kernel/dma/swiotlb.c
> > +++ b/kernel/dma/swiotlb.c
> > @@ -659,9 +659,9 @@ size_t swiotlb_max_mapping_size(struct device *dev)
> >       return ((size_t)IO_TLB_SIZE) * IO_TLB_SEGSIZE;
> >   }
> >
> > -bool is_swiotlb_active(void)
> > +bool is_swiotlb_active(struct device *dev)
> >   {
> > -     return io_tlb_default_mem != NULL;
> > +     return get_io_tlb_mem(dev) != NULL;
> >   }
> >   EXPORT_SYMBOL_GPL(is_swiotlb_active);
> >
> >