From: Sakari Ailus <sakari.ailus@linux.intel.com>
To: Hans Verkuil <hverkuil@xs4all.nl>, linux-media@vger.kernel.org
Cc: pawel@osciak.com, m.szyprowski@samsung.com,
kyungmin.park@samsung.com, sumit.semwal@linaro.org,
robdclark@gmail.com, daniel.vetter@ffwll.ch, labbott@redhat.com
Subject: Re: [RFC RESEND 07/11] vb2: dma-contig: Remove redundant sgt_base field
Date: Tue, 15 Sep 2015 11:26:58 +0300 [thread overview]
Message-ID: <55F7D652.9020903@linux.intel.com> (raw)
In-Reply-To: <55F30F50.6090902@xs4all.nl>
Hi Hans,
Hans Verkuil wrote:
> On 09/11/2015 01:50 PM, Sakari Ailus wrote:
>> The struct vb2_dc_buf contains two struct sg_table fields: sgt_base and
>> dma_sgt. The former is used by DMA-BUF buffers whereas the latter is used
>> by USERPTR.
>>
>> Unify the two, leaving dma_sgt.
>>
>> MMAP buffers do not need cache flushing since they have been allocated
>> using dma_alloc_coherent().
>
> I would have to see this again after it is rebased on 4.3-rc1. That will contain
> Jan Kara's vb2 changes which might well affect this patch.
Ok. I'll do that.
>
> Are there use-cases where we want to allocate non-coherent memory? I know we
> don't support this today, but is this something we might want in the future?
Yes. Not all hardware supports coherent memory access, not even on x86.
Or coherent memory (sometimes uncached!) may be slower than non-coherent
access, including the time it takes to flush the cache first.
--
Kind regards,
Sakari Ailus
sakari.ailus@linux.intel.com
next prev parent reply other threads:[~2015-09-15 8:27 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-11 11:50 [RFC RESEND 00/11] vb2: Handle user cache hints, allow drivers to choose cache coherency Sakari Ailus
2015-09-11 11:50 ` [RFC RESEND 01/11] vb2: Rename confusingly named internal buffer preparation functions Sakari Ailus
2015-09-11 15:57 ` Hans Verkuil
2016-12-15 15:40 ` Laurent Pinchart
2015-09-11 11:50 ` [RFC RESEND 02/11] vb2: Move buffer cache synchronisation to prepare from queue Sakari Ailus
2015-09-11 16:11 ` Hans Verkuil
2015-09-11 11:50 ` [RFC RESEND 03/11] vb2: Move cache synchronisation from buffer done to dqbuf handler Sakari Ailus
2015-09-11 16:25 ` Hans Verkuil
2015-09-15 7:51 ` Sakari Ailus
2016-12-15 23:47 ` Laurent Pinchart
2015-09-11 11:50 ` [RFC RESEND 04/11] v4l: Unify cache management hint buffer flags Sakari Ailus
2015-09-11 16:26 ` Hans Verkuil
2015-09-11 16:44 ` Hans Verkuil
2016-12-15 20:15 ` Laurent Pinchart
2016-12-17 0:35 ` Sakari Ailus
2015-09-11 11:50 ` [RFC RESEND 05/11] v4l2-core: Don't sync cache for a buffer if so requested Sakari Ailus
2015-09-11 17:12 ` Hans Verkuil
2015-09-15 8:22 ` Sakari Ailus
2015-09-15 9:06 ` Hans Verkuil
2016-12-15 20:37 ` Laurent Pinchart
2016-12-17 0:36 ` Sakari Ailus
2015-09-11 11:50 ` [RFC RESEND 06/11] vb2: Improve struct vb2_mem_ops documentation; alloc and put are for MMAP Sakari Ailus
2015-09-11 17:13 ` Hans Verkuil
2016-12-15 20:50 ` Laurent Pinchart
2015-09-11 11:50 ` [RFC RESEND 07/11] vb2: dma-contig: Remove redundant sgt_base field Sakari Ailus
2015-09-11 17:28 ` Hans Verkuil
2015-09-15 8:26 ` Sakari Ailus [this message]
2016-12-15 21:08 ` Laurent Pinchart
2016-12-17 0:40 ` Sakari Ailus
2015-09-11 11:50 ` [RFC RESEND 08/11] vb2: dma-contig: Move vb2_dc_get_base_sgt() up Sakari Ailus
2016-12-15 21:12 ` Laurent Pinchart
2015-09-11 11:50 ` [RFC RESEND 09/11] vb2: dma-contig: Don't warn on failure in obtaining scatterlist Sakari Ailus
2016-12-15 21:13 ` Laurent Pinchart
2015-09-11 11:50 ` [RFC RESEND 10/11] vb2: dma-contig: Let drivers decide DMA attrs of MMAP and USERPTR bufs Sakari Ailus
2016-12-15 21:40 ` Laurent Pinchart
2015-09-11 11:50 ` [RFC RESEND 11/11] vb2: dma-contig: Add WARN_ON_ONCE() to check for potential bugs Sakari Ailus
2016-12-15 21:57 ` Laurent Pinchart
2016-12-17 0:50 ` Sakari Ailus
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