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

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Date:   Mon, 26 Aug 2019 08:41:40 -0700
From:   Scott Branden <scott.branden@...adcom.com>
To:     Takashi Iwai <tiwai@...e.de>
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

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.
>
>>> Also it won't work for the compressed firmware files as-is.
>> Although unnecessary, seems to work fine in the fw_run_tests.sh with
>> "both" and "xzonly" options.
> This looks also suspicious.  Loading a part of the file from the
> middle and decompression won't work together, from obvious reasons.
I don't know what the underlying mechanisms are doing right now.
If they decompress the whole file then that is why it's working.
An obvious improvement that could be made later is to only read
a portion of the file before writing it into the buffer in the non-xz case.
>
> If the test passes, it means that the test itself is more likely
> incorrect, I'm afraid.
Then all of the tests for "both" and "xzonly" could be broken.
>
>
> thanks,
>
> Takashi
Regards,
  Scott