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

Lucas De Marchi
2022-01-27T09:12:53Z

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
>