linux-kernel - Re: [PATCH v2] ata: libata-scsi: Fix CDL control

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Message-ID: <1d33a2b0-8811-474a-8399-71eeaa05a2ea@kernel.org>
Date: Thu, 14 Aug 2025 11:28:02 +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 v2] ata: libata-scsi: Fix CDL control

On 8/14/25 11:22 AM, Igor Pylypiv wrote:
> Delete extra checks for the ATA_DFLAG_CDL_ENABLED flag that 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 enabled already.
> 
> Fixes: 17e897a45675 ("ata: libata-scsi: Improve CDL control")
> Signed-off-by: Igor Pylypiv <ipylypiv@...gle.com>

Thanks. This looks good.

Of note though, is that this is all due to the fact that we set or clear the
flag irrespective of the result of the SET_FEATURE command, which may actually
fail... But we do not have a simple way to wait for that command to complete
first before manipulating the flag. This will need some bigger fixes later :)

> ---
> 
> Changes from v1:
> - Changed the patch from revert to fixup.
> - Restored debug logs and the comment about mutual exclusivity with
>   NCQ priority.
> - Dropped cc to stable and added fixes tag instead.
> 
>  drivers/ata/libata-scsi.c | 11 +++--------
>  1 file changed, 3 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> index 57f674f51b0c..2ded5e476d6e 100644
> --- a/drivers/ata/libata-scsi.c
> +++ b/drivers/ata/libata-scsi.c
> @@ -3904,21 +3904,16 @@ 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;
> +		/* Disable CDL */
>  		ata_dev_dbg(dev, "Disabling CDL\n");
>  		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.
> +		 * Enable CDL. Since CDL is mutually exclusive with NCQ
> +		 * priority, allow this only if NCQ priority is disabled.
>  		 */
> -		if (dev->flags & ATA_DFLAG_CDL_ENABLED)
> -			return 0;
>  		if (dev->flags & ATA_DFLAG_NCQ_PRIO_ENABLED) {
>  			ata_dev_err(dev,
>  				"NCQ priority must be disabled to enable CDL\n");


-- 
Damien Le Moal
Western Digital Research