Re: [PATCH 2/7] firmware: add offset to request_firmware_into_buf

From: Scott Branden <scott.branden@broadcom.com>
To: Takashi Iwai <tiwai@suse.de>
Cc: Luis Chamberlain <mcgrof@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	David Brown <david.brown@linaro.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Shuah Khan <shuah@kernel.org>,
	bjorn.andersson@linaro.org,
	Shuah Khan <skhan@linuxfoundation.org>,
	Arnd Bergmann <arnd@arndb.de>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
	linux-fsdevel@vger.kernel.org,
	BCM Kernel Feedback <bcm-kernel-feedback-list@broadcom.com>,
	Olof Johansson <olof@lixom.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Dan Carpenter <dan.carpenter@oracle.com>,
	Colin Ian King <colin.king@canonical.com>,
	Kees Cook <keescook@chromium.org>,
	linux-kselftest@vger.kernel.org
Subject: Re: [PATCH 2/7] firmware: add offset to request_firmware_into_buf
Date: Mon, 26 Aug 2019 10:24:22 -0700
Message-ID: <b440f372-45be-c06c-94a1-44ae6b1e7eb8@broadcom.com> (raw)
In-Reply-To: <s5ho90byhnv.wl-tiwai@suse.de>

Hi Takashi,

On 2019-08-26 10:12 a.m., Takashi Iwai wrote:
> 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()...
Yes, we access the PCI region directly in the driver and thus also 
through request_firmware_into_buf.
I will admit I am not familiar with every subtlety of PCI accesses. Any 
comments to the Valkyrie driver in this patch series are appreciated.
But not all drivers need to work on all architectures. I can add a 
depends on x86 64bit architectures to the driver to limit it to such.
>
>
> thanks,
>
> Takashi