Re: [PATCH 19/28] gpu/drm: remove the powerpc hack in drm_legacy_sg_alloc

From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Daniel Vetter <daniel@ffwll.ch>, Christoph Hellwig <hch@lst.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	"K. Y. Srinivasan" <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	Wei Liu <wei.liu@kernel.org>,
	x86@kernel.org, David Airlie <airlied@linux.ie>,
	Laura Abbott <labbott@redhat.com>,
	Sumit Semwal <sumit.semwal@linaro.org>,
	Sakari Ailus <sakari.ailus@linux.intel.com>,
	Minchan Kim <minchan@kernel.org>, Nitin Gupta <ngupta@vflare.org>,
	Robin Murphy <robin.murphy@arm.com>,
	Christophe Leroy <christophe.leroy@c-s.fr>,
	Peter Zijlstra <peterz@infradead.org>,
	linuxppc-dev@lists.ozlabs.org, linux-hyperv@vger.kernel.org,
	dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org,
	linux-arch@vger.kernel.org, linux-mm@kvack.org,
	iommu@lists.linux-foundation.org,
	linux-arm-kernel@lists.infradead.org, linux-s390@vger.kernel.org,
	bpf@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 19/28] gpu/drm: remove the powerpc hack in drm_legacy_sg_alloc
Date: Thu, 09 Apr 2020 18:54:01 +1000	[thread overview]
Message-ID: <eb48f7b6327e482ea9911b129210c0417ab48345.camel@kernel.crashing.org> (raw)
In-Reply-To: <20200408122504.GO3456981@phenom.ffwll.local>

On Wed, 2020-04-08 at 14:25 +0200, Daniel Vetter wrote:
> On Wed, Apr 08, 2020 at 01:59:17PM +0200, Christoph Hellwig wrote:
> > If this code was broken for non-coherent caches a crude powerpc hack
> > isn't going to help anyone else.  Remove the hack as it is the last
> > user of __vmalloc passing a page protection flag other than PAGE_KERNEL.
> 
> Well Ben added this to make stuff work on ppc, ofc the home grown dma
> layer in drm from back then isn't going to work in other places. I guess
> should have at least an ack from him, in case anyone still cares about
> this on ppc. Adding Ben to cc.

This was due to some drivers (radeon ?) trying to use vmalloc pages for
coherent DMA, which means on those 4xx powerpc's need to be non-cached.

There were machines using that (440 based iirc), though I honestly
can't tell if anybody still uses any of it.

Cheers,
Ben.

> -Daniel
> 
> > 
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > ---
> >  drivers/gpu/drm/drm_scatter.c | 11 +----------
> >  1 file changed, 1 insertion(+), 10 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_scatter.c b/drivers/gpu/drm/drm_scatter.c
> > index ca520028b2cb..f4e6184d1877 100644
> > --- a/drivers/gpu/drm/drm_scatter.c
> > +++ b/drivers/gpu/drm/drm_scatter.c
> > @@ -43,15 +43,6 @@
> >  
> >  #define DEBUG_SCATTER 0
> >  
> > -static inline void *drm_vmalloc_dma(unsigned long size)
> > -{
> > -#if defined(__powerpc__) && defined(CONFIG_NOT_COHERENT_CACHE)
> > -	return __vmalloc(size, GFP_KERNEL, pgprot_noncached_wc(PAGE_KERNEL));
> > -#else
> > -	return vmalloc_32(size);
> > -#endif
> > -}
> > -
> >  static void drm_sg_cleanup(struct drm_sg_mem * entry)
> >  {
> >  	struct page *page;
> > @@ -126,7 +117,7 @@ int drm_legacy_sg_alloc(struct drm_device *dev, void *data,
> >  		return -ENOMEM;
> >  	}
> >  
> > -	entry->virtual = drm_vmalloc_dma(pages << PAGE_SHIFT);
> > +	entry->virtual = vmalloc_32(pages << PAGE_SHIFT);
> >  	if (!entry->virtual) {
> >  		kfree(entry->busaddr);
> >  		kfree(entry->pagelist);
> > -- 
> > 2.25.1
> > 
> 
> 