Re: [Intel-gfx] [PATCH 02/19] dma-buf-map: Add helper to initialize second map

From: Lucas De Marchi <lucas.demarchi@intel.com>
To: "Christian König" <christian.koenig@amd.com>
Cc: linaro-mm-sig@lists.linaro.org, intel-gfx@lists.freedesktop.org,
	linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
	linux-media@vger.kernel.org,
	Thomas Zimmermann <tzimmermann@suse.de>
Subject: Re: [Intel-gfx] [PATCH 02/19] dma-buf-map: Add helper to initialize second map
Date: Thu, 27 Jan 2022 01:12:47 -0800	[thread overview]
Message-ID: <20220127091247.3uqi5zhesqtecbsw@ldmartin-desk2> (raw)
In-Reply-To: <3c6a9126-bf88-0f29-425f-36748271c179@amd.com>

On Thu, Jan 27, 2022 at 09:55:05AM +0100, Christian König wrote:
>Am 27.01.22 um 09:18 schrieb Lucas De Marchi:
>>On Thu, Jan 27, 2022 at 09:02:54AM +0100, Christian König wrote:
>>>Am 27.01.22 um 08:57 schrieb Lucas De Marchi:
>>>>On Thu, Jan 27, 2022 at 08:27:11AM +0100, Christian König wrote:
>>>>>Am 26.01.22 um 21:36 schrieb Lucas De Marchi:
>>>>>>[SNIP]
>>>>humn... not sure if I was  clear. There is no importer and 
>>>>exporter here.
>>>
>>>Yeah, and exactly that's what I'm pointing out as problem here.
>>>
>>>You are using the inter driver framework for something internal to 
>>>the driver. That is an absolutely clear NAK!
>>>
>>>We could discuss that, but you guys are just sending around 
>>>patches to do this without any consensus that this is a good idea.
>>
>>s/you guys/you/ if you have to blame anyone - I'm the only s-o-b in
>>these patches. I'm sending these to _build consensus_ on what may be 
>>a good
>>use for it showing a real problem it's helping to fix.
>
>Well a cover letter would have been helpful, my impression was that 
>you have a larger set and just want to upstream some minor DMA-buf 
>changes necessary for it.

I missed adding this sentence to the cover letter, as my impression was that
dma-buf-map was already used outside inter-driver framework. But there
is actually a cover letter:

https://lore.kernel.org/all/20220126203702.1784589-1-lucas.demarchi@intel.com/

And looking at it now, it seems I missed adding Thomas Zimmermann to Cc.

>
>Now I know why people are bugging me all the time to add cover letters 
>to add more context to my sets.
>
>>
>>From its documentation:
>>
>> * The type :c:type:`struct dma_buf_map <dma_buf_map>` and its 
>>helpers are
>> * actually independent from the dma-buf infrastructure. When 
>>sharing buffers
>> * among devices, drivers have to know the location of the memory to 
>>access
>> * the buffers in a safe way. :c:type:`struct dma_buf_map <dma_buf_map>`
>> * solves this problem for dma-buf and its users. If other drivers or
>> * sub-systems require similar functionality, the type could be 
>>generalized
>> * and moved to a more prominent header file.
>>
>>if there is no consensus and a better alternative, I'm perfectly fine in
>>throwing it out and using the better approach.
>
>When Thomas Zimmermann upstreamed the dma_buf_map work we had a 
>discussion if that shouldn't be independent of the DMA-buf framework.
>
>The consensus was that as soon as we have more widely use for it this 
>should be made independent. So basically that is what's happening now.
>
>I suggest the following approach:
>1. Find a funky name for this, something like iomem_, kiomap_ or similar.

iosys_map?

>2. Separate this from all you driver dependent work and move the 
>dma_buf_map structure out of DMA-buf into this new whatever_ prefix.

should this be a follow up to the driver work or a prerequisite?

thanks
Lucas De Marchi

>3. Ping Thomas, LKML, me and probably a couple of other core people if 
>this is the right idea or not.
>4. Work on dropping the map parameter from dma_buf_vunmap(). This is 
>basically why we can't modify the pointers returned from 
>dma_buf_vmap() and has already cause a few problems with 
>dma_buf_map_incr().
>
>Regards,
>Christian.
>
>>
>>Lucas De Marchi
>