linux-kernel - Re: [PATCH 3/3] ahci: Document the loss of hotplug by new LPM policy

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Message-ID: <Yo3xGRqkfrh7joIR@infradead.org>
Date:   Wed, 25 May 2022 02:04:25 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Mario Limonciello <mario.limonciello@....com>
Cc:     Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        "open list:LIBATA SUBSYSTEM (Serial and Parallel ATA drivers)" 
        <linux-ide@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>, hdegoede@...hat.com
Subject: Re: [PATCH 3/3] ahci: Document the loss of hotplug by new LPM policy

On Tue, May 24, 2022 at 12:05:08PM -0500, Mario Limonciello wrote:
> Per AHCI spec v1.3.1, "7.3 Native Hot Plug Support", once LPM is
> enabled hotplug support needs to be disabled.
> 
> The LPM code always followed this and disabled the port when no
> drives were connected, but as more machines will be exposed to
> this code it might be an unexpected behavior to some users.
> 
> Add a note to parameter documentation to explain the new behavior.
> 
> Link: https://bugs.launchpad.net/bugs/1971576
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 9e6bd212004d..4dcd9a3ba4a5 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -279,6 +279,13 @@
>  			3 => Medium power with Device Initiated PM enabled
>  			4 => Minimum power
>  
> +			NOTE: Enabling LPM when no drive is connected will disable
> +			the port which means hotplug will not work.
> +
> +			If hotplug is an important use case, this can be modified

This has two overly long lines.