linux-kernel - Re: Do Qualcomm drivers use DMA buffers for request_firmware_into

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Message-ID: <20180607161847.GN510@tuxbook-pro>
Date:   Thu, 7 Jun 2018 09:18:47 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Rik van Riel <riel@...riel.com>,
        Laura Abbott <labbott@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Martijn Coenen <maco@...roid.com>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Vikram Mulukutla <markivx@...eaurora.org>,
        Arve Hj?nnev?g <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        linux-security-module@...r.kernel.org,
        Chris Wright <chrisw@...s-sol.org>,
        David Howells <dhowells@...hat.com>,
        Alan Cox <alan@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        platform-driver-x86@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Jones <pjones@...hat.com>,
        Dave Olsthoorn <dave@...aar.me>,
        Will Deacon <will.deacon@....com>,
        Andy Lutomirski <luto@...nel.org>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Josh Triplett <josh@...htriplett.org>,
        dmitry.torokhov@...il.com, Jonathan Corbet <corbet@....net>,
        mfuzzey@...keon.com, Kalle Valo <kvalo@...eaurora.org>,
        Arend Van Spriel <arend.vanspriel@...adcom.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        nbroeking@...com, Torsten Duwe <duwe@...e.de>, x86@...nel.org,
        linux-efi <linux-efi@...r.kernel.org>,
        "open list:ANDROID DRIVERS" <devel@...verdev.osuosl.org>,
        linux-arm-msm@...r.kernel.org
Subject: Re: Do Qualcomm drivers use DMA buffers for
 request_firmware_into_buf()?

On Wed 06 Jun 13:32 PDT 2018, Luis R. Rodriguez wrote:

> 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...
> 

The patch at the top of this thread doesn't interest me and you didn't
bother sending your question To me.

As a matter of fact I'm confused to what the actual question is.

> 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!
> 

Where do you want to put this?

> 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?
> 

>From what I can see [0] says is to use READING_FIRMWARE_PREALLOC_BUFFER
regardless of where the memory comes from.

Regards,
Bjorn

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