From: "Andrew F. Davis" <afd@ti.com>
To: Liam Mark <lmark@codeaurora.org>
Cc: Christoph Hellwig <hch@infradead.org>,
Laura Abbott <labbott@redhat.com>, <sumit.semwal@linaro.org>,
<arve@android.com>, <tkjos@android.com>, <maco@android.com>,
<joel@joelfernandes.org>, <christian@brauner.io>,
<devel@driverdev.osuosl.org>, <dri-devel@lists.freedesktop.org>,
<linaro-mm-sig@lists.linaro.org>, <linux-kernel@vger.kernel.org>,
<john.stultz@linaro.org>
Subject: Re: [PATCH 3/4] dma-buf: add support for mapping with dma mapping attributes
Date: Mon, 21 Jan 2019 14:24:09 -0600 [thread overview]
Message-ID: <4925c9db-fc73-1ccb-1766-ef68d014d55a@ti.com> (raw)
In-Reply-To: <alpine.DEB.2.10.1901211214570.11004@lmark-linux.qualcomm.com>
On 1/21/19 2:20 PM, Liam Mark wrote:
> On Mon, 21 Jan 2019, Andrew F. Davis wrote:
>
>> On 1/21/19 1:44 PM, Liam Mark wrote:
>>> On Mon, 21 Jan 2019, Christoph Hellwig wrote:
>>>
>>>> On Sat, Jan 19, 2019 at 08:50:41AM -0800, Laura Abbott wrote:
>>>>>> And who is going to decide which ones to pass? And who documents
>>>>>> which ones are safe?
>>>>>>
>>>>>> I'd much rather have explicit, well documented dma-buf flags that
>>>>>> might get translated to the DMA API flags, which are not error checked,
>>>>>> not very well documented and way to easy to get wrong.
>>>>>>
>>>>>
>>>>> I'm not sure having flags in dma-buf really solves anything
>>>>> given drivers can use the attributes directly with dma_map
>>>>> anyway, which is what we're looking to do. The intention
>>>>> is for the driver creating the dma_buf attachment to have
>>>>> the knowledge of which flags to use.
>>>>
>>>> Well, there are very few flags that you can simply use for all calls of
>>>> dma_map*. And given how badly these flags are defined I just don't want
>>>> people to add more places where they indirectly use these flags, as
>>>> it will be more than enough work to clean up the current mess.
>>>>
>>>> What flag(s) do you want to pass this way, btw? Maybe that is where
>>>> the problem is.
>>>>
>>>
>>> The main use case is for allowing clients to pass in
>>> DMA_ATTR_SKIP_CPU_SYNC in order to skip the default cache maintenance
>>> which happens in dma_buf_map_attachment and dma_buf_unmap_attachment. In
>>> ION the buffers aren't usually accessed from the CPU so this allows
>>> clients to often avoid doing unnecessary cache maintenance.
>>>
>>
>> How can a client know that no CPU access has occurred that needs to be
>> flushed out?
>>
>
> I have left this to clients, but if they own the buffer they can have the
> knowledge as to whether CPU access is needed in that use case (example for
> post-processing).
>
> For example with the previous version of ION we left all decisions of
> whether cache maintenance was required up to the client, they would use
> the ION cache maintenance IOCTL to force cache maintenance only when it
> was required.
> In these cases almost all of the access was being done by the device and
> in the rare cases CPU access was required clients would initiate the
> required cache maintenance before and after the CPU access.
>
I think we have different definitions of "client", I'm talking about the
DMA-BUF client (the importer), that is who can set this flag. It seems
you mean the userspace application, which has no control over this flag.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
> a Linux Foundation Collaborative Project
>
next prev parent reply other threads:[~2019-01-21 20:24 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-18 18:37 [PATCH 0/4] ION stability and perf changes Liam Mark
2019-01-18 18:37 ` [PATCH 1/4] staging: android: ion: Support cpu access during dma_buf_detach Liam Mark
2019-01-18 19:34 ` Andrew F. Davis
2019-01-18 20:40 ` Laura Abbott
2019-01-18 18:37 ` [PATCH 2/4] staging: android: ion: Restrict cache maintenance to dma mapped memory Liam Mark
2019-01-18 20:20 ` Andrew F. Davis
2019-01-18 21:18 ` Liam Mark
2019-01-29 23:44 ` Liam Mark
2019-01-30 11:31 ` Brian Starkey
2019-02-06 15:40 ` [Linaro-mm-sig] " Ørjan Eide
2019-02-07 7:31 ` Christoph Hellwig
2019-02-07 15:45 ` Ørjan Eide
2019-02-28 23:49 ` Liam Mark
2019-01-30 14:31 ` Andrew F. Davis
2019-01-18 18:37 ` [PATCH 3/4] dma-buf: add support for mapping with dma mapping attributes Liam Mark
2019-01-18 20:48 ` Laura Abbott
2019-01-18 21:32 ` Liam Mark
2019-01-18 22:45 ` Laura Abbott
2019-01-19 10:25 ` Christoph Hellwig
2019-01-19 16:50 ` Laura Abbott
2019-01-21 8:30 ` Christoph Hellwig
2019-01-21 19:44 ` Liam Mark
2019-01-21 19:49 ` Andrew F. Davis
2019-01-21 20:20 ` Liam Mark
2019-01-21 20:24 ` Andrew F. Davis [this message]
2019-01-21 22:18 ` Liam Mark
2019-01-22 15:42 ` Andrew F. Davis
2019-01-22 22:47 ` Liam Mark
2019-01-21 21:30 ` Christoph Hellwig
2019-01-21 22:14 ` Liam Mark
2019-01-21 21:29 ` Christoph Hellwig
2019-01-21 22:12 ` Liam Mark
2019-01-22 16:06 ` Andrew F. Davis
2019-01-22 22:50 ` Liam Mark
2019-01-18 18:37 ` [PATCH 4/4] staging: android: ion: Support " Liam Mark
2019-01-21 12:19 ` Brian Starkey
2019-01-22 22:37 ` Liam Mark
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