linux-kernel - Re: [PATCH] Revert "ata: libata-scsi: Improve CDL control"

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Message-ID: <9dde49e5-4368-402f-8cc2-797ac08c0e8a@kernel.org>
Date: Thu, 14 Aug 2025 08:08:37 +0900
From: Damien Le Moal <dlemoal@...nel.org>
To: Igor Pylypiv <ipylypiv@...gle.com>, Niklas Cassel <cassel@...nel.org>
Cc: linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Revert "ata: libata-scsi: Improve CDL control"

On 8/14/25 5:46 AM, Igor Pylypiv wrote:
> This reverts commit 17e897a456752ec9c2d7afb3d9baf268b442451b.

A full revert is not nice. See below.

Also please change the patch title to:

ata: libata-scsi: Fix CDL control

Or similar.

And do not send the patch to stable@...r.kernel.org. It will be picked up if
you add the Fixes tag (see below).

> 
> The extra checks for the ATA_DFLAG_CDL_ENABLED flag prevent SET FEATURES
> command from being issued to a drive when NCQ commands are active.
> 
> ata_mselect_control_ata_feature() sets / clears the ATA_DFLAG_CDL_ENABLED
> flag during the translation of MODE SELECT to SET FEATURES. If SET FEATURES
> gets deferred due to outstanding NCQ commands, the original MODE SELECT
> command will be re-queued. When the re-queued MODE SELECT goes through
> the ata_mselect_control_ata_feature() translation again, SET FEATURES
> will not be issued because ATA_DFLAG_CDL_ENABLED has been already set or
> cleared by the initial translation of MODE SELECT.
> 
> The ATA_DFLAG_CDL_ENABLED checks in ata_mselect_control_ata_feature()
> are safe to remove because scsi_cdl_enable() implements a similar logic
> that avoids enabling CDL if it has been already enabled.
> 

Please add "Fixes: 17e897a45675 ("ata: libata-scsi: Improve CDL control") here.

> Cc: stable@...r.kernel.org
> Signed-off-by: Igor Pylypiv <ipylypiv@...gle.com>
> ---
>  drivers/ata/libata-scsi.c | 14 ++------------
>  1 file changed, 2 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> index 57f674f51b0c..856eabfd5a17 100644
> --- a/drivers/ata/libata-scsi.c
> +++ b/drivers/ata/libata-scsi.c
> @@ -3904,27 +3904,17 @@ static int ata_mselect_control_ata_feature(struct ata_queued_cmd *qc,
>  	/* Check cdl_ctrl */
>  	switch (buf[0] & 0x03) {
>  	case 0:
> -		/* Disable CDL if it is enabled */
> -		if (!(dev->flags & ATA_DFLAG_CDL_ENABLED))
> -			return 0;
> -		ata_dev_dbg(dev, "Disabling CDL\n");

Please keep this debug message and move it below the comment.

> +		/* Disable CDL */
>  		cdl_action = 0;
>  		dev->flags &= ~ATA_DFLAG_CDL_ENABLED;
>  		break;
>  	case 0x02:
> -		/*
> -		 * Enable CDL if not already enabled. Since this is mutually
> -		 * exclusive with NCQ priority, allow this only if NCQ priority
> -		 * is disabled.
> -		 */
> -		if (dev->flags & ATA_DFLAG_CDL_ENABLED)
> -			return 0;
> +		/* Enable CDL T2A/T2B: NCQ priority must be disabled */

T2A/T2B is for SCSI, not ATA. So let's not mention that. I prefer that the
comment keeps the "mutually exclusive" mention, so something like:

		*
		* Enable CDL. Since this is mutually exclusive with the NCQ
		* priority feature set, allow this only if NCQ priority is
		* disabled.
		*/

>  		if (dev->flags & ATA_DFLAG_NCQ_PRIO_ENABLED) {
>  			ata_dev_err(dev,
>  				"NCQ priority must be disabled to enable CDL\n");
>  			return -EINVAL;
>  		}
> -		ata_dev_dbg(dev, "Enabling CDL\n");

And please keep this debug message.

>  		cdl_action = 1;
>  		dev->flags |= ATA_DFLAG_CDL_ENABLED;
>  		break;


-- 
Damien Le Moal
Western Digital Research