Messages in this thread | | | From | Andy Shevchenko <> | Date | Wed, 27 Feb 2019 16:15:37 +0200 | Subject | Re: [PATCH] lib/scatterlist: introduce sg_nents_for_dma() helper |
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On Wed, Feb 27, 2019 at 2:26 PM Ardelean, Alexandru <Alex.Ardelean@analog.com> wrote: > > On Wed, 2019-02-27 at 11:46 +0200, Andy Shevchenko wrote: > > [External] > > > > > > +Cc Vinod > > > > On Wed, Feb 27, 2019 at 11:45 AM Andy Shevchenko > > <andy.shevchenko@gmail.com> wrote: > > > > > > On Wed, Feb 27, 2019 at 10:51 AM Alexandru Ardelean > > > <alexandru.ardelean@analog.com> wrote: > > > > > > > > From: Andy Shevchenko <andy.shevchenko@gmail.com> > > > > > > > > Sometimes the user needs to split each entry on the mapped scatter > > > > list > > > > due to DMA length constrains. This helper returns a number of > > > > entities > > > > assuming that each of them is not bigger than supplied maximum > > > > length. > > > > > > > > Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com> > > > > Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com> > > > > > > Hmm... Usually we don't accept generic API without users. > > > Do you have any use case in mind? > > Yep: this one: > https://patchwork.kernel.org/patch/10814527/ > > But, I can rework this patch to work without the helper.
Ah, okay, worth to mention this in comments (in addition to what you put about the patch below).
> > > > Patch was sent in 2016 initially to the DMA engine sub-system. > > > > Link: > > > > https://patchwork.kernel.org/patch/9389821/ > > > > This was part of a larger series: > > > > > > > > https://patchwork.kernel.org/project/linux-dmaengine/list/?q=sg_nents_for_dma&archive=both&series=&submitter=&delegate=&state=* > > > > > > > > I'm not sure if this is supposed to go into DMAEngine or > > > > lib/scatterlist. > > > > It doesn't look like lib/scatterlist is managed by DMAEngine, so (by > > > > using > > > > the `get_maintainers.pl` script) I'm sending this patch to this group > > > > of > > > > parties. > > > > > > The problem the patch tried to solve is much deeper and correct > > > solution should be more generic, i.e. > > > each channel should provide a set of parameters, such as DMA segment > > > size, to the users (via DMA engine API) and users should prepare the > > > SG list according to the limits of the channel. > > > In that case we don't need to re-split/re-allocate given SG list at > > > all, which would simplify DMA slave drivers and their users. > > > > > I don't think I managed to follow [or find] the full length of that > discussion. Or, the conclusion wasn't that obvious to me, from what I > found. > I assumed this may have been dropped/forgotten. > > In any case, I am fine with just reworking.
It's fine to apply it, my point that it help to solve a symptom in a short-term (however this short-term can be easily a long one due to no guarantee that all drivers using SG for DMA will be converted). So, please, update the comments and resubmit as a new version.
-- With Best Regards, Andy Shevchenko
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