linux-kernel - Re: [RFC 1/2] firmware class: Add stream

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Message-ID: <CANk1AXSWFYbZ0aoSMZYC1=5OkPvjtbLHO-ZtSSgLrAOi7C5SbA@mail.gmail.com>
Date:   Wed, 22 Mar 2017 19:34:41 -0500
From:   Alan Tull <delicious.quinoa@...il.com>
To:     "Li, Yi" <yi1.li@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        ming.lei@...onical.com, mcgrof@...nel.org,
        atull <atull@...nsource.altera.com>,
        Moritz Fischer <moritz.fischer@...us.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-fpga@...r.kernel.org
Subject: Re: [RFC 1/2] firmware class: Add stream_firmware API.

On Wed, Mar 22, 2017 at 5:05 PM, Li, Yi <yi1.li@...ux.intel.com> wrote:
> Alan
>
>
> On 3/20/2017 1:34 PM, Alan Tull wrote:
>>
>> On Mon, Mar 20, 2017 at 1:00 PM, Alan Tull <delicious.quinoa@...il.com>
>> wrote:
>>
>>>> +int
>>>> +stream_firmware(const struct firmware **firmware_p, const char *name,
>>>> +                struct device *device, size_t offset, size_t length)
>>>> +{
>>>> +       size_t ret;
>>>> +
>>>> +       /* Need to pin this module until return */
>>>> +       __module_get(THIS_MODULE);
>>>> +       ret = _stream_firmware(firmware_p, name, device, NULL, 0,
>>>> +                               FW_OPT_UEVENT | FW_OPT_NO_WARN, offset,
>>>> length);
>>
>> IIUC, here you are setting size == 0 and buf == NULL  to prevent
>> _request_firmware_prepare from attempting to load from built in
>> firmware.
>>
>> So three of the parameters buf, size, and opt_flags are fixed and
>> don't need to be passed to _stream_firmware().
>
>
> Sure.
>
>> Alternatively, I wonder how hard it would be to code this so that the
>> streaming interface will fall back and successfully get the built in
>> or cached firmware if it exists and stream it out in PAGE_SIZE chunks.
>
>
> That's an interesting idea, I will try it out and submit patch for review
> later. On another hand, if the kernel already cache the whole firmware
> image, why should we use streaming instead of regular request_firmware?

The caller doesn't know whether the firmware is cached or not.  The
caller just wants the firmware if it exists, wherever it is.  If that can be
made automatic then the caller doesn't have to first attempt stream_firmware
and then if that fails fall back to calling request_firmware.

>
>>
>> Alan Tull
>> --
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>
>