linux-kernel - Re: [PATCH 04/14] firmware_loader: add built-in firmware kconfig entry

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Date:   Mon, 11 Oct 2021 10:35:37 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     bp@...e.de, akpm@...ux-foundation.org, josh@...htriplett.org,
        rishabhb@...eaurora.org, kubakici@...pl, maco@...roid.com,
        david.brown@...aro.org, bjorn.andersson@...aro.org,
        linux-wireless@...r.kernel.org, keescook@...omium.org,
        shuah@...nel.org, mfuzzey@...keon.com, zohar@...ux.vnet.ibm.com,
        dhowells@...hat.com, pali.rohar@...il.com, tiwai@...e.de,
        arend.vanspriel@...adcom.com, zajec5@...il.com, nbroeking@...com,
        broonie@...nel.org, dmitry.torokhov@...il.com, dwmw2@...radead.org,
        torvalds@...ux-foundation.org, Abhay_Salunke@...l.com,
        jewalt@...innovations.com, cantabile.desu@...il.com, ast@...com,
        andresx7@...il.com, dan.rue@...aro.org, brendanhiggins@...gle.com,
        yzaikin@...gle.com, sfr@...b.auug.org.au, rdunlap@...radead.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 04/14] firmware_loader: add built-in firmware kconfig
 entry

On Tue, Oct 05, 2021 at 04:30:06PM +0200, Greg KH wrote:
> On Fri, Sep 17, 2021 at 11:22:16AM -0700, Luis R. Rodriguez wrote:
> > From: Luis Chamberlain <mcgrof@...nel.org>
> > 
> > The built-in firmware is always supported when a user enables
> > FW_LOADER=y today, that is, it is built-in to the kernel. When the
> > firmware loader is built as a module, support for built-in firmware
> > is skipped. This requirement is not really clear to users or even
> > developers.
> > 
> > Also, by default the EXTRA_FIRMWARE is always set to an empty string
> > and so by default we really have nothing built-in to that kernel's
> > sections for built-in firmware, so today a all FW_LOADER=y kernels
> > spins their wheels on an empty set of built-in firmware for each
> > firmware request with no true need for it.
> > 
> > Add a new kconfig entry to represent built-in firmware support more
> > clearly. This let's knock 3 birds with one stone:
> > 
> >  o Clarifies that support for built-in firmware requires the
> >    firmware loader to be built-in to the kernel
> > 
> >  o By default we now always skip built-in firmware even if a FW_LOADER=y
> > 
> >  o This also lets us make it clear that the EXTRA_FIRMWARE_DIR
> >    kconfig entry is only used for built-in firmware
> > 
> > Reviewed-by: Borislav Petkov <bp@...e.de>
> > Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
> > ---
> >  .../driver-api/firmware/built-in-fw.rst       |  2 ++
> >  Documentation/x86/microcode.rst               |  5 ++--
> >  drivers/base/firmware_loader/Kconfig          | 25 +++++++++++++------
> >  drivers/base/firmware_loader/Makefile         |  3 +--
> >  drivers/base/firmware_loader/main.c           |  4 +--
> >  5 files changed, 26 insertions(+), 13 deletions(-)
> > 
> > diff --git a/Documentation/driver-api/firmware/built-in-fw.rst b/Documentation/driver-api/firmware/built-in-fw.rst
> > index bc1c961bace1..9dd2b1df44f0 100644
> > --- a/Documentation/driver-api/firmware/built-in-fw.rst
> > +++ b/Documentation/driver-api/firmware/built-in-fw.rst
> > @@ -8,6 +8,7 @@ the filesystem. Instead, firmware can be looked for inside the kernel
> >  directly. You can enable built-in firmware using the kernel configuration
> >  options:
> >  
> > +  * CONFIG_FW_LOADER_BUILTIN
> >    * CONFIG_EXTRA_FIRMWARE
> >    * CONFIG_EXTRA_FIRMWARE_DIR
> >  
> > @@ -17,6 +18,7 @@ into the kernel with CONFIG_EXTRA_FIRMWARE:
> >  * Speed
> >  * Firmware is needed for accessing the boot device, and the user doesn't
> >    want to stuff the firmware into the boot initramfs.
> > +* Testing built-in firmware
> >  
> >  Even if you have these needs there are a few reasons why you may not be
> >  able to make use of built-in firmware:
> > diff --git a/Documentation/x86/microcode.rst b/Documentation/x86/microcode.rst
> > index a320d37982ed..d199f0b98869 100644
> > --- a/Documentation/x86/microcode.rst
> > +++ b/Documentation/x86/microcode.rst
> > @@ -114,11 +114,12 @@ Builtin microcode
> >  =================
> >  
> >  The loader supports also loading of a builtin microcode supplied through
> > -the regular builtin firmware method CONFIG_EXTRA_FIRMWARE. Only 64-bit is
> > -currently supported.
> > +the regular builtin firmware method using CONFIG_FW_LOADER_BUILTIN and
> > +CONFIG_EXTRA_FIRMWARE. Only 64-bit is currently supported.
> >  
> >  Here's an example::
> >  
> > +  CONFIG_FW_LOADER_BUILTIN=y
> >    CONFIG_EXTRA_FIRMWARE="intel-ucode/06-3a-09 amd-ucode/microcode_amd_fam15h.bin"
> >    CONFIG_EXTRA_FIRMWARE_DIR="/lib/firmware"
> >  
> > diff --git a/drivers/base/firmware_loader/Kconfig b/drivers/base/firmware_loader/Kconfig
> > index 5b24f3959255..de4fcd9d41f3 100644
> > --- a/drivers/base/firmware_loader/Kconfig
> > +++ b/drivers/base/firmware_loader/Kconfig
> > @@ -29,8 +29,10 @@ if FW_LOADER
> >  config FW_LOADER_PAGED_BUF
> >  	bool
> >  
> > -config EXTRA_FIRMWARE
> > -	string "Build named firmware blobs into the kernel binary"
> > +config FW_LOADER_BUILTIN
> > +	bool "Enable support for built-in firmware"
> > +	default n
> 
> n is always the default, no need to list it again.

Oh, alrighty, I'll remove that line.

> > +	depends on FW_LOADER=y
> 
> I don't see what this gets us to add another config option.  Are you
> making things easier later on?

This makes a few things clearer for both developers and users.
The code in question is a *feature* *only* when FW_LOADER=y, by
adding a new kconfig to represent this and clearly makeing it
depend on FW_LOADER=y it let's us:

  o Clarify that support for built-in firmware requires
    the firmware loader to be built-in to the kernel
  o By default we now always skip built-in firmware even if a FW_LOADER=y
  o This also lets us make it clear that the EXTRA_FIRMWARE_DIR
    kconfig entry is only used for built-in firmware

The above is not easily obvious to developers (including myself when
I was reviewing this code) or users without this new kconfig entry.

Should I re-send by just removing the one line you asked for?

  Luis