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

From: Scott Branden
Date: Mon Aug 26 2019 - 11:41:49 EST

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 with fallbacks.
But how? You patch doesn't change anything about the fallback loading
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 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.