linux-kernel - Re: [PATCH] net: stmmac: dwmac-meson8b: fix meson8b_devm_clk_prepare

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Date:   Fri, 4 Nov 2022 22:02:02 +0100
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Andrew Lunn <andrew@...n.ch>,
        "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: stmmac: dwmac-meson8b: fix meson8b_devm_clk_prepare_enable()

Hello Rasmus,

Thanks for your patch!
It would be great if you could Cc linux-amlogic@...ts.infradead.org in
v2 of this patch, so other Amlogic SoC maintainers can also provide
their feedback.

On Fri, Nov 4, 2022 at 9:30 AM Rasmus Villemoes
<linux@...musvillemoes.dk> wrote:
>
> There are two problems with meson8b_devm_clk_prepare_enable(),
> introduced in a54dc4a49045 (net: stmmac: dwmac-meson8b: Make the clock
> enabling code re-usable):
>
> - It doesn't pass the clk argument, but instead always the
>   rgmii_tx_clk of the device.
Indeed, this is a problem - thanks for fixing this!

> - It silently ignores the return value of devm_add_action_or_reset().
This second part is not so easy.
The thought process back when this code was implemented was: let's
continue loading of the driver even if devm_add_action_or_reset()
fails as this just means during shutdown/rmmod we don't disable all
clocks.
If we want to propagate the error code returned by
devm_add_action_or_reset() then we also need to do the clean up within
meson8b_devm_clk_prepare_enable(), meaning we need to call
clk_disable_unprepare() in case devm_add_action_or_reset() failed.
Your change just propagates the error code without disabling and
unpreparing the clock.

[...]
> The latter means the callers could
> end up with the clock not actually prepared/enabled.
In my opinion this statement is not correct: even if
devm_add_action_or_reset() fails the clock will be prepared and
enabled (by clk_prepare_enable() right before).

Personally I would just change the clk argument and keep the return 0.
What do you think?


Best regards,
Martin