linux-kernel - Re: [PATCH 19/28] gpu/drm: remove the powerpc hack in drm_legacy_sg

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Message-ID: <d4a82787-5dd2-ccde-79b4-ff44848ba04e@gmx.net>
Date:   Thu, 9 Apr 2020 13:46:26 +0200
From:   Gerhard Pircher <gerhard_pircher@....net>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Daniel Vetter <daniel@...ll.ch>, Christoph Hellwig <hch@....de>
Cc:     linux-hyperv@...r.kernel.org, David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org, linux-mm@...ck.org,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        linux-arch@...r.kernel.org, linux-s390@...r.kernel.org,
        Wei Liu <wei.liu@...nel.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Laura Abbott <labbott@...hat.com>,
        Nitin Gupta <ngupta@...are.org>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        linaro-mm-sig@...ts.linaro.org, bpf@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Robin Murphy <robin.murphy@....com>,
        linux-kernel@...r.kernel.org, Minchan Kim <minchan@...nel.org>,
        iommu@...ts.linux-foundation.org,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 19/28] gpu/drm: remove the powerpc hack in
 drm_legacy_sg_alloc

Am 09.04.20 um 10:54 schrieb Benjamin Herrenschmidt:
> 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.
The first-gen amigaone platform (6xx/book32s) uses the radeon driver
together with non-coherent DMA. However this only ever worked reliably
for DRI1.

br,
Gerhard

> Cheers,
> Ben.
>
>> -Daniel
>>
>>>
>>> Signed-off-by: Christoph Hellwig <hch@....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
>>>
>>
>>
>