linux-kernel - Re: [PATCH] clocksource/drivers/riscv: Refuse to probe on T-Head

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Date:   Thu, 9 Feb 2023 23:40:45 +0000
From:   Conor Dooley <conor@...nel.org>
To:     Palmer Dabbelt <palmer@...osinc.com>
Cc:     linux-riscv@...ts.infradead.org, daniel.lezcano@...aro.org,
        tglx@...utronix.de, Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>, aou@...s.berkeley.edu,
        linux-kernel@...r.kernel.org, linux@...osinc.com
Subject: Re: [PATCH] clocksource/drivers/riscv: Refuse to probe on T-Head

Hey Palmer,

On Thu, Feb 09, 2023 at 03:23:02PM -0800, Palmer Dabbelt wrote:
> From: Palmer Dabbelt <palmer@...osinc.com>
> 
> As of d9f15a9de44a ("Revert "clocksource/drivers/riscv: Events are
> stopped during CPU suspend"") this driver no longer functions correctly
> for the T-Head firmware.  That shouldn't impact any users, as we've got
> a functioning driver that's higher priority, but let's just be safe and
> ban it from probing at all.
> 
> Signed-off-by: Palmer Dabbelt <palmer@...osinc.com>
> ---
> This feel super ugly to me, but I'm not sure how to do this more
> cleanly.  I'm not even sure if it's necessary, but I just ran back into
> the driver reviewing some other patches so I figured I'd say something.

I'm not super sure what you're trying to fix here. That revert went
through to restore behaviour for the SiFive stuff that do deliver events
in suspend.

Subsequently, we added a DT property (probably the wrong one tbh, but
that's all said and done now) that communicates that a timer is
incapable of waking the cpus. See commit 98ce3981716c ("dt-bindings:
timer: Add bindings for the RISC-V timer device") & the full patchset is
at:
https://lore.kernel.org/linux-riscv/20230103141102.772228-1-apatel@ventanamicro.com/

AFAIU, the binding for the T-HEAD clint was only accepted in the last
week & there's nothing actually using this timer. IIRC, when I wanted to
test the timer, Samuel cooked me up a WIP openSBI etc to enable it.

So ye, I don't think this is needed fortunately!

Cheers,
Conor.

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