linux-kernel - Re: [PATCH 2/7] firmware: add offset to request_firmware_into

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Date:   Mon, 26 Aug 2019 19:12:52 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Scott Branden <scott.branden@...adcom.com>
Cc:     Luis Chamberlain <mcgrof@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Brown <david.brown@...aro.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Shuah Khan <shuah@...nel.org>, bjorn.andersson@...aro.org,
        Shuah Khan <skhan@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>,
        Olof Johansson <olof@...om.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Colin Ian King <colin.king@...onical.com>,
        Kees Cook <keescook@...omium.org>,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 2/7] firmware: add offset to request_firmware_into_buf

On Mon, 26 Aug 2019 17:41:40 +0200,
Scott Branden wrote:
> 
> HI Takashi,
> 
> On 2019-08-26 8:20 a.m., Takashi Iwai wrote:
> > On Fri, 23 Aug 2019 21:44:42 +0200,
> > Scott Branden wrote:
> >> Hi Takashi,
> >>
> >> Thanks for review.  comments below.
> >>
> >> On 2019-08-23 3:05 a.m., Takashi Iwai wrote:
> >>> On Thu, 22 Aug 2019 21:24:46 +0200,
> >>> Scott Branden wrote:
> >>>> Add offset to request_firmware_into_buf to allow for portions
> >>>> of firmware file to be read into a buffer.  Necessary where firmware
> >>>> needs to be loaded in portions from file in memory constrained systems.
> >>> AFAIU, this won't work with the fallback user helper, right?
> >> Seems to work fine in the fw_run_tests.sh with fallbacks.
> > But how?  You patch doesn't change anything about the fallback loading
> > mechanism.
> Correct - I didn't change any of the underlying mechanisms,
> so however request_firmware_into_buf worked before it still does.
> >   Or, if the expected behavior is to load the whole content
> > and then copy a part, what's the merit of this API?
> The merit of the API is that the entire file is not copied into a buffer.
> In my use case, the buffer is a memory region in PCIe space that isn't
> even large enough for the whole file.  So the only way to get the file
> is to read it
> in portions.

BTW: does the use case above mean that the firmware API directly
writes onto the given PCI iomem region?  If so, I'm not sure whether
it would work as expected on all architectures.  There must be a
reason of the presence of iomem-related API like memcpy_toio()...


thanks,

Takashi