linux-kernel - Re: [PATCH v2 2/2] firmware: exynos-acpm: allow use during system shutdown

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Message-ID: <be580155-372f-445b-b9d1-2dc4fbf1c3a1@kernel.org>
Date: Tue, 25 Mar 2025 08:57:25 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: André Draszik <andre.draszik@...aro.org>,
 Tudor Ambarus <tudor.ambarus@...aro.org>,
 Alim Akhtar <alim.akhtar@...sung.com>
Cc: Peter Griffin <peter.griffin@...aro.org>,
 Will McVicker <willmcvicker@...gle.com>, kernel-team@...roid.com,
 linux-kernel@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 2/2] firmware: exynos-acpm: allow use during system
 shutdown

On 24/03/2025 16:34, André Draszik wrote:
> +static bool acpm_may_sleep(void)
> +{
> +	return system_state <= SYSTEM_RUNNING ||
> +		(IS_ENABLED(CONFIG_PREEMPT_COUNT) ? preemptible() : !irqs_disabled());
> +}
> +
>  /**
>   * acpm_dequeue_by_polling() - RX dequeue by polling.
>   * @achan:	ACPM channel info.
> @@ -300,7 +314,10 @@ static int acpm_dequeue_by_polling(struct acpm_chan *achan,
>  			return 0;
>  
>  		/* Determined experimentally. */
> -		usleep_range(20, 30);
> +		if (!acpm_may_sleep())
> +			udelay(10);
> +		else

... and what do you do if IRQs get disabled exactly in this moment? This
is just racy. You cannot check for a condition and assume it will be
valid for whatever time you want it to be valid.

What happens if system_state is changed to shutdown in this particular
moment? How did you prevent this from happening?

> +			usleep_range(20, 30);
>  	} while (ktime_before(ktime_get(), timeout));
>  
>  	dev_err(dev, "Timeout! ch:%u s:%u bitmap:%lx.\n",
> 


Best regards,
Krzysztof