linux-kernel - Re: [PATCH v2 1/2] dt-bindings: remoteproc: qcom: Add firmware bindings for Q6V5

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Message-ID: <20190105015430.GA67838@google.com>
Date:   Fri, 4 Jan 2019 17:54:32 -0800
From:   Brian Norris <briannorris@...omium.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Sibi Sankar <sibis@...eaurora.org>, david.brown@...aro.org,
        robh+dt@...nel.org, mark.rutland@....com, andy.gross@...aro.org,
        akdwived@...eaurora.org, clew@...eaurora.org,
        linux-kernel@...r.kernel.org, linux-arm-msm-owner@...r.kernel.org,
        ohad@...ery.com, linux-remoteproc@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v2 1/2] dt-bindings: remoteproc: qcom: Add firmware
 bindings for Q6V5

Hi again,

On Thu, Jan 03, 2019 at 04:11:58PM -0800, Brian Norris wrote:
> On Thu, Jan 03, 2019 at 04:01:45PM -0800, Bjorn Andersson wrote:
> > I share your concern about this, but I came to suggest this as the
> > driver cares about platforms but the firmware is (often?)
> > device/product-specific.
> > 
> > E.g. we will serve the MTP and Pixel 3 with the qcom,sdm845-adsp-pas
> > compatible, but they are unlikely to run the same adsp firmware. This
> > allows the individual dtb to specify which firmware the driver should
> > use.
> 
> I understand this, but that still doesn't mean we should be suggesting
> each DTB to clutter the top-level firmware search path, especially since
> lazy people will probably just use "modem.mdt" and similar. That means
> you no longer can ship the same rootfs that supports both QCOM and
> <other> modems, if <other> modem also uses the same lazy format.
> 
> It seems like a much better practice to at least enforce a particular
> prefix to things. e.g., the driver could assume:
> 
>   qcom/sdm845-adsp-pas/ (or if you must, just qcom/)
> 
> and your DTB only gets to add .../<your-string-here> to that path.
> 
> In case it isn't clear: I think it's also severely misguided that the
> existing driver gets away with lines like
> 
> 	request_firmware(&fw, "modem.mdt", ...);
> 
> today ;)

To add to my thoughts, since I think maybe Sibi was a little unclear of
my thoughts:

One of my primary concerns with the existing approach is that it's
basically a complete free-for-all. We should have some minimal standards
(enforced in code) such that our DTB can never point us at something
like /lib/firmware/<other-vendor>/foo.bin (or /lib/firmware/modem.mdt;
or lots of other bad examples). This could probably be done simply by
always prefixing 'qcom/' (I don't remember -- does request_firmware()
follow '..'? e.g., 'firmware-name = "../bar/foo.bin"'.)

As a bonus: it would be very nice if we can provide a little more
structure by default, and avoid arbitrary hierarchy in the DTS. That's
where I brought up ath10k's "variant" as an example; if we can use
'compatible' to capture most of this particular Hexagon core's
properties, then we only leave a single level of variability to the DTS.

But I might be off-base with the "bonus" paragraph. So I'd also be
somewhat happy with something much less ambitious, like just a built-in
prefix ('qcom/').

And you can also just ignore my thoughts entirely (and I'll be even less
happy), since Rob did already provide his Reviewed-by ;) I mostly wanted
to give food for thought, in the hopes that something in here would help
improve this a bit.

Regards,
Brian