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

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Date: Fri, 6 Oct 2023 13:47:25 +0200
From: Alexandre TORGUE <alexandre.torgue@...s.st.com>
To: Ben Wolsieffer <ben.wolsieffer@...ring.com>,
        Jacob Keller
	<jacob.e.keller@...el.com>
CC: <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <netdev@...r.kernel.org>, Jose Abreu <joabreu@...opsys.com>,
        "David S.
 Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        "Jakub
 Kicinski" <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
        Maxime Coquelin
	<mcoquelin.stm32@...il.com>,
        Christophe Roullier <christophe.roullier@...com>
Subject: Re: [PATCH net] net: stmmac: dwmac-stm32: fix resume on STM32 MCU

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@...ring.com>
>>> ---
>>
>> 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@hefring.com/T/
> 
> Thanks, Ben