Re: [PATCH net] net: stmmac: dwmac-stm32: fix resume on STM32 MCU

[Alexandre TORGUE]

On 10/2/23 15:54, Ben Wolsieffer wrote:
> Hi Jacob,
>
> On Fri, Sep 29, 2023 at 10:48:47AM -0700, Jacob Keller wrote:
> > On 9/27/2023 10:57 AM, Ben Wolsieffer wrote:
> > > The STM32MP1 keeps clk_rx enabled during suspend, and therefore the
> > > driver does not enable the clock in stm32_dwmac_init() if the device was
> > > suspended. The problem is that this same code runs on STM32 MCUs, which
> > > do disable clk_rx during suspend, causing the clock to never be
> > > re-enabled on resume.
> > >
> > > This patch adds a variant flag to indicate that clk_rx remains enabled
> > > during suspend, and uses this to decide whether to enable the clock in
> > > stm32_dwmac_init() if the device was suspended.
> >
> > Why not just keep clk_rx enabled unconditionally or unconditionally stop
> > it during suspend? I guess that might be part of a larger cleanup and
> > has more side effects?
>
> Ideally, you want to turn off as many clocks as possible in suspend to
> save power. I'm assuming there is some hardware reason the STM32MP1
> needs the RX clock on during suspend, but it was not explained in the
> original patch. Without more information, I'm trying to maintain the
> existing behavior.

Sorry for this late answer. We could need RX clock for WOL support.

> > > This approach fixes this specific bug with limited opportunity for
> > > unintended side-effects, but I have a follow up patch that will refactor
> > > the clock configuration and hopefully make it less error prone.
> >
> > I'd guess the follow-up refactor would target next?
> >
> > > Fixes: 6528e02cc9ff ("net: ethernet: stmmac: add adaptation for stm32mp157c.")
> > > Signed-off-by: Ben Wolsieffer <ben.wolsieffer@xxxxxxxxxxx>
> > > ---
> >
> > This seems pretty small and targeted so it does make sense to me as a
> > net fix, but it definitely feels like a workaround.
> >
> > I look forward to reading the cleanup patch mentioned.
>
> Sorry, I should have linked this when I re-posted this patch for
> net, but I previously submitted this patch as part of a series with
> the cleanup but was asked to split them up for net and net-next.
> Personally, I would be fine with them going into net-next together (or
> squashed).
>
> The original series can be found here:
> https://lore.kernel.org/linux-arm-kernel/20230919164535.128125-3-ben.wolsieffer@xxxxxxxxxxx/T/
>
> Thanks, Ben