linux-kernel - Re: [PATCH v7 10/24] wfx: add fwio.c/fwio.h

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Date:   Thu, 07 Oct 2021 11:35:06 +0200
From:   Jérôme Pouiller <jerome.pouiller@...abs.com>
To:     Kalle Valo <kvalo@...eaurora.org>
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "David S . Miller" <davem@...emloft.net>,
        devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        linux-mmc@...r.kernel.org,
        Pali Rohár <pali@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH v7 10/24] wfx: add fwio.c/fwio.h

On Thursday 7 October 2021 10:08:53 CEST Kalle Valo wrote:
> Jérôme Pouiller <jerome.pouiller@...abs.com> writes:
> > On Friday 1 October 2021 13:58:38 CEST Kalle Valo wrote:
> >> Jerome Pouiller <Jerome.Pouiller@...abs.com> writes:
> >>
> >> > From: Jérôme Pouiller <jerome.pouiller@...abs.com>
> >> >
> >> > Signed-off-by: Jérôme Pouiller <jerome.pouiller@...abs.com>
> >>
> >> [...]
> >>
> >> > +static int get_firmware(struct wfx_dev *wdev, u32 keyset_chip,
> >> > +                     const struct firmware **fw, int *file_offset)
> >> > +{
> >> > +     int keyset_file;
> >> > +     char filename[256];
> >> > +     const char *data;
> >> > +     int ret;
> >> > +
> >> > +     snprintf(filename, sizeof(filename), "%s_%02X.sec",
> >> > +              wdev->pdata.file_fw, keyset_chip);
> >> > +     ret = firmware_request_nowarn(fw, filename, wdev->dev);
> >> > +     if (ret) {
> >> > +             dev_info(wdev->dev, "can't load %s, falling back to %s.sec\n",
> >> > +                      filename, wdev->pdata.file_fw);
> >> > +             snprintf(filename, sizeof(filename), "%s.sec",
> >> > +                      wdev->pdata.file_fw);
> >> > +             ret = request_firmware(fw, filename, wdev->dev);
> >> > +             if (ret) {
> >> > +                     dev_err(wdev->dev, "can't load %s\n", filename);
> >> > +                     *fw = NULL;
> >> > +                     return ret;
> >> > +             }
> >> > +     }
> >>
> >> How is this firmware file loading supposed to work? If I'm reading the
> >> code right, the driver tries to load file "wfm_wf200_??.sec" but in
> >> linux-firmware the file is silabs/wfm_wf200_C0.sec:
> >>
> >> https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/tree/silabs
> >>
> >> That can't work automatically, unless I'm missing something of course.
> >
> > The firmware are signed. "C0" is the key used to sign this firmware. This
> > key must match with the key burned into the chip. Fortunately, the driver
> > is able to read the key accepted by the chip and automatically choose the
> > right firmware.
> >
> > We could imagine to add a attribute in the DT to choose the firmware to
> > load. However, it would be a pity to have to specify it manually whereas
> > the driver is able to detect it automatically.
> >
> > Currently, the only possible key is C0. However, it exists some internal
> > parts with other keys. In addition, it is theoretically possible to ask
> > to Silabs to burn parts with a specific key in order to improve security
> > of a product.
> >
> > Obviously, for now, this feature mainly exists for the Silabs firmware
> > developers who have to work with other keys.
> 
> My point above was about the directory "silabs". If I read the code
> correctly, wfx driver tries to load "foo.bin" but in the linux-firmware
> file is "silabs/foo.bin". So the should also include directory name in
> the request and use "silabs/foo.bin".

Oh! Absolutely. I had never noticed my firmware was not in silabs/ on my
test setup.

[...]
-- 
Jérôme Pouiller