Re: [PATCH 01/12] soc: qcom: add firmware name helper

[Kalle Valo <kvalo@kernel.org>]

Bjorn Andersson <andersson@kernel.org> writes:

> On Mon, May 27, 2024 at 02:42:44PM GMT, Dmitry Baryshkov wrote:
>
>> On Thu, 23 May 2024 at 01:48, Bjorn Andersson <quic_bjorande@quicinc.com> wrote:
>> >
>> > On Tue, May 21, 2024 at 03:08:31PM +0200, Dmitry Baryshkov wrote:
>> > > On Tue, 21 May 2024 at 13:20, Kalle Valo <kvalo@kernel.org> wrote:
>> > > >
>> > > > Dmitry Baryshkov <dmitry.baryshkov@linaro.org> writes:
>> > > >
>> > > > > On Tue, 21 May 2024 at 12:52, <neil.armstrong@linaro.org> wrote:
>> > > > >>
>> > > > >> On 21/05/2024 11:45, Dmitry Baryshkov wrote:
>> > > > >> > Qualcomm platforms have different sets of the firmware files, which
>> > > > >> > differ from platform to platform (and from board to board, due to the
>> > > > >> > embedded signatures). Rather than listing all the firmware files,
>> > > > >> > including full paths, in the DT, provide a way to determine firmware
>> > > > >> > path based on the root DT node compatible.
>> > > > >>
>> > > > >> Ok this looks quite over-engineered but necessary to handle the legacy,
>> > > > >> but I really think we should add a way to look for a board-specific path
>> > > > >> first and fallback to those SoC specific paths.
>> > > > >
>> > > > > Again, CONFIG_FW_LOADER_USER_HELPER => delays.
>> > > >
>> > > > To me this also looks like very over-engineered, can you elaborate more
>> > > > why this is needed? Concrete examples would help to understand better.
>> > >
>> > > Sure. During the meeting last week Arnd suggested evaluating if we can
>> > > drop firmware-name from the board DT files. Several reasons for that:
>> > > - DT should describe the hardware, not the Linux-firmware locations
>> > > - having firmware name in DT complicates updating the tree to use
>> > > different firmware API (think of mbn vs mdt vs any other format)
>> > > - If the DT gets supplied by the vendor (e.g. for
>> > > SystemReady-certified devices), there should be a sync between the
>> > > vendor's DT, linux kernel and the rootfs. Dropping firmware names from
>> > > DT solves that by removing one piece of the equation
>> > >
>> > > Now for the complexity of the solution. Each SoC family has their own
>> > > firmware set. This includes firmware for the DSPs, for modem, WiFi
>> > > bits, GPU shader, etc.
>> > > For the development boards these devices are signed by the testing key
>> > > and the actual signature is not validated against the root of trust
>> > > certificate.
>> > > For the end-user devices the signature is actually validated against
>> > > the bits fused to the SoC during manufacturing process. CA certificate
>> > > (and thus the fuses) differ from vendor to vendor (and from the device
>> > > to device)
>> > >
>> > > Not all of the firmware files are a part of the public linux-firmware
>> > > tree. However we need to support the rootfs bundled with the firmware
>> > > for different platforms (both public and vendor). The non-signed files
>> > > come from the Adreno GPU and can be shared between platforms. All
>> > > other files are SoC-specific and in some cases device-specific.
>> > >
>> > > So for example the SDM845 db845c (open device) loads following firmware files:
>> > > Not signed:
>> > > - qcom/a630_sqe.fw
>> > > - qcom/a630_gmu.bin
>> > >
>> > > Signed, will work for any non-secured sdm845 device:
>> > > - qcom/sdm845/a630_zap.mbn
>> > > - qcom/sdm845/adsp.mbn
>> > > - qcom/sdm845/cdsp.mbn
>> > > - qcom/sdm485/mba.mbn
>> > > - qcom/sdm845/modem.mbn
>> > > - qcom/sdm845/wlanmdsp.mbn (loaded via TQFTP)
>> > > - qcom/venus-5.2/venus.mbn
>> > >
>> > > Signed, works only for DB845c.
>> > > - qcom/sdm845/Thundercomm/db845c/slpi.mbn
>> > >
>> > > In comparison, the SDM845 Pixel-3 phone (aka blueline) should load the
>> > > following firmware files:
>> > > - qcom/a630_sqe.fw (the same, non-signed file)
>> > > - qcom/a630_gmu.bin (the same, non-signed file)
>> > > - qcom/sdm845/Google/blueline/a630_zap.mbn
>> >
>> > How do you get from "a630_zap.mbn" to this? By extending the lookup
>> > table for every target, or what am I missing?
>> 
>> More or less so. Matching the root OF node gives us the firmware
>> location, then it gets prepended to all firmware targets. Not an ideal
>> solution, as there is no fallback support, but at least it gives us
>> some points to discuss (and to decide whether to move to some
>> particular direction or to abandon the idea completely, making Arnd
>> unhappy again).
>> 
>
> I understand the desire to not put linux-firmware-specific paths in the
> DeviceTree

Me too.

> but I think I'm less keen on having a big lookup table in the
> kernel...

Yeah, also for me this feels wrong. But on the other hand I don't have
anything better to suggest either...

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