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Message-ID: <CAFp+6iGNw7tjFLf-i7KM3agqgJPhsWGK2Ga=wAEU+_EfCJO1Cw@mail.gmail.com>
Date: Thu, 29 Nov 2018 15:13:25 +0530
From: Vivek Gautam <vivek.gautam@...eaurora.org>
To: Tomasz Figa <tfiga@...omium.org>
Cc: David Airlie <airlied@...ux.ie>, Rob Clark <robdclark@...il.com>,
open list <linux-kernel@...r.kernel.org>,
freedreno <freedreno@...ts.freedesktop.org>,
dri-devel <dri-devel@...ts.freedesktop.org>,
linux-arm-msm <linux-arm-msm@...r.kernel.org>,
Jordan Crouse <jcrouse@...eaurora.org>,
Sean Paul <seanpaul@...omium.org>
Subject: Re: [PATCH v2 1/1] drm: msm: Replace dma_map_sg with dma_sync_sg*
Hi Tomasz,
On Wed, Nov 28, 2018 at 8:39 AM Tomasz Figa <tfiga@...omium.org> wrote:
>
> Hi Vivek,
>
> On Tue, Nov 27, 2018 at 6:37 AM Vivek Gautam
> <vivek.gautam@...eaurora.org> wrote:
> >
> > dma_map_sg() expects a DMA domain. However, the drm devices
> > have been traditionally using unmanaged iommu domain which
> > is non-dma type. Using dma mapping APIs with that domain is bad.
> >
> > Replace dma_map_sg() calls with dma_sync_sg_for_device{|cpu}()
> > to do the cache maintenance.
> >
> > Signed-off-by: Vivek Gautam <vivek.gautam@...eaurora.org>
> > Suggested-by: Tomasz Figa <tfiga@...omium.org>
> > Cc: Rob Clark <robdclark@...il.com>
> > Cc: Jordan Crouse <jcrouse@...eaurora.org>
> > Cc: Sean Paul <seanpaul@...omium.org>
> > ---
> >
> > Changes since v1:
> > - Addressed Jordan's and Tomasz's comments for
> > - moving sg dma addresses preparation out of the coditional
> > check to the main path so we do it irrespective of whether
> > the buffer is cached or uncached.
> > - Enhance the comment to explain this dma addresses prepartion.
> >
>
> Thanks for the patch. Some comments inline.
>
> > drivers/gpu/drm/msm/msm_gem.c | 31 ++++++++++++++++++++++---------
> > 1 file changed, 22 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
> > index 00c795ced02c..1811ac23a31c 100644
> > --- a/drivers/gpu/drm/msm/msm_gem.c
> > +++ b/drivers/gpu/drm/msm/msm_gem.c
> > @@ -81,6 +81,8 @@ static struct page **get_pages(struct drm_gem_object *obj)
> > struct drm_device *dev = obj->dev;
> > struct page **p;
> > int npages = obj->size >> PAGE_SHIFT;
> > + struct scatterlist *s;
> > + int i;
> >
> > if (use_pages(obj))
> > p = drm_gem_get_pages(obj);
> > @@ -104,12 +106,21 @@ static struct page **get_pages(struct drm_gem_object *obj)
> > return ptr;
> > }
> >
> > - /* For non-cached buffers, ensure the new pages are clean
> > + /*
> > + * dma_sync_sg_*() flush the physical pages, so point
> > + * sg->dma_address to the physical ones for the right behavior.
>
> The two halves of the sequence don't really relate to each other. An
> sglist has the `page` field for the purpose of pointing to physical
> pages. The `dma_address` field is for DMA addresses, which are not
> equivalent to physical addresses. I'd rewrite it like this;
I guess I was lenient in using the physical pages and dma address words.
>
> /*
> * Some implementations of the DMA mapping ops expect
> * physical addresses of the pages to be stored as DMA
> * addresses of the sglist entries. To work around it,
> * set them here explicitly.
> */
Will update as suggested.
> > + */
> > + for_each_sg(msm_obj->sgt->sgl, s, msm_obj->sgt->nents, i)
> > + sg_dma_address(s) = sg_phys(s);
> > +
> > + /*
> > + * For non-cached buffers, ensure the new pages are clean
> > * because display controller, GPU, etc. are not coherent:
> > */
> > - if (msm_obj->flags & (MSM_BO_WC|MSM_BO_UNCACHED))
> > - dma_map_sg(dev->dev, msm_obj->sgt->sgl,
> > - msm_obj->sgt->nents, DMA_BIDIRECTIONAL);
> > + if (msm_obj->flags & (MSM_BO_WC | MSM_BO_UNCACHED))
> > + dma_sync_sg_for_device(dev->dev, msm_obj->sgt->sgl,
> > + msm_obj->sgt->nents,
> > + DMA_TO_DEVICE);
>
> Why changing from DMA_BIDIRECTIONAL?
Yea, I went back and checked that we wanted to do this for both.
Will keep DMA_BIDIRECTIONAL intact.
>
> > }
> >
> > return msm_obj->pages;
> > @@ -133,14 +144,16 @@ static void put_pages(struct drm_gem_object *obj)
> >
> > if (msm_obj->pages) {
> > if (msm_obj->sgt) {
> > - /* For non-cached buffers, ensure the new
> > + /*
> > + * For non-cached buffers, ensure the new
> > * pages are clean because display controller,
> > * GPU, etc. are not coherent:
> > */
> > - if (msm_obj->flags & (MSM_BO_WC|MSM_BO_UNCACHED))
> > - dma_unmap_sg(obj->dev->dev, msm_obj->sgt->sgl,
> > - msm_obj->sgt->nents,
> > - DMA_BIDIRECTIONAL);
> > + if (msm_obj->flags & (MSM_BO_WC | MSM_BO_UNCACHED))
> > + dma_sync_sg_for_cpu(obj->dev->dev,
> > + msm_obj->sgt->sgl,
> > + msm_obj->sgt->nents,
> > + DMA_FROM_DEVICE);
>
> Ditto.
Sure, will change this as well.
Thanks & Regards
Vivek
>
> Best regards,
> Tomasz
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