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Date: Wed, 6 Jun 2018 22:32:57 +0200
From: "Luis R. Rodriguez" <mcgrof@kernel.org>
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Subject: Do Qualcomm drivers use DMA buffers for request_firmware_into_buf()?
Message-ID: <20180606203257.GH4511@wotan.suse.de>
References: <20180408174014.21908-3-hdegoede@redhat.com>
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 <20180424234219.GX14440@wotan.suse.de>
 <1524632409.3371.48.camel@linux.vnet.ibm.com>
 <20180425175557.GY14440@wotan.suse.de>
 <CAB0TPYGnCu+anWHBGvkaigxD--8uHQaQJ2c62kegJ7mTqvkmnA@mail.gmail.com>
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On Fri, Jun 01, 2018 at 09:23:46PM +0200, Luis R. Rodriguez wrote:
> On Tue, May 08, 2018 at 03:38:05PM +0000, Luis R. Rodriguez wrote:
> > On Fri, May 04, 2018 at 12:44:37PM -0700, Martijn Coenen wrote:
> > > 
> > > I think the Qualcomm folks owning this (Andy, David, Bjorn, already
> > > cc'd here) are better suited to answer that question.
> > 
> > Andy, David, Bjorn?
> 
> Andy, David, Bjorn?

A month now with no answer...

Perhaps someone who has this hardware can find out empirically for us, as
follows (mm folks is this right?):

page = virt_to_page(address);
if (!page)
   fail closed...
if (page_zone(page) == ZONE_DMA || page_zone(page) == ZONE_DMA32)
	this is a DMA buffer
else
	not DMA!

Note that when request_firmware_into_buf() was being reviewed Mimi had asked back
in 2016 [0] that if a DMA buffer was going to be used READING_FIRMWARE_DMA should be
used otherwise READING_FIRMWARE_PREALLOC_BUFFER was fine.

If it is a DMA buffer *now*, why / how did this change?

[0] https://patchwork.kernel.org/patch/9074611/

  Luis