Re: [PATCH v5 5/6] ata: libata-scsi: probe additional LUNs for multi-LUN ATAPI devices

[Damien Le Moal]

On 2026/05/12 22:27, Phil Pemberton wrote:
> After LUN 0 is added for an ATAPI device, check its BLIST_FORCELUN
> flag.  If set, bump dev->nr_luns to the host's max_lun so the LUN
> routing in atapi_xlat() accepts the probe INQUIRYs, then call
> scsi_scan_target() with SCAN_WILD_CARD to trigger the SCSI layer's
> built-in sequential LUN scan for that target only.  This probes
> LUNs 1..shost->max_lun, driven by the libata atapi_max_lun module
> parameter.
> 
> Devices without BLIST_FORCELUN (the vast majority of ATAPI devices)
> are left with only LUN 0 -- no sequential scan is triggered, so
> single-LUN devices like the iHAS124 DVD writer are completely
> unaffected.
> 
> Non-responding LUNs (PQ=0/PDT=0x1f) are silently skipped by
> scsi_probe_and_add_lun() when BLIST_NO_LUN_1F is set on the device
> via scsi_devinfo.
> 
> Signed-off-by: Phil Pemberton <philpem@xxxxxxxxxxxxx>
> ---
>  drivers/ata/libata-scsi.c | 27 +++++++++++++++++++++++----
>  1 file changed, 23 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> index 2d714efc855f..a6f5557014c7 100644
> --- a/drivers/ata/libata-scsi.c
> +++ b/drivers/ata/libata-scsi.c
> @@ -26,6 +26,7 @@
>  #include <scsi/scsi_device.h>
>  #include <scsi/scsi_tcq.h>
>  #include <scsi/scsi_transport.h>
> +#include <scsi/scsi_devinfo.h>
>  #include <linux/libata.h>
>  #include <linux/hdreg.h>
>  #include <linux/uaccess.h>
> @@ -4745,12 +4746,30 @@ void ata_scsi_scan_host(struct ata_port *ap, int sync)
>  			sdev = __scsi_add_device(ap->scsi_host, channel, id, 0,
>  						 NULL);
>  			if (!IS_ERR(sdev)) {
> -				dev->sdev[0] = sdev;

Maybe reverse this condition and do a continue here. That will avoid the
additional indent level, which will make the hunk below a little more pretty.

			if (IS_ERR(sdev)) {
				dev->sdev[0] = NULL;
				continue;
			}

			/*
			 * For multi-LUN ATAPI (BLIST_FORCELUN), bump...
			 ...

> -				ata_scsi_assign_ofnode(dev, ap);
> +				/*
> +				 * For multi-LUN ATAPI (BLIST_FORCELUN), bump
> +				 * dev->nr_luns to the host max so the LUN
> +				 * routing in atapi_xlat() accepts the probe
> +				 * INQUIRYs to LUN > 0, then trigger the
> +				 * sequential scan.  pdt_1f_for_no_lun, set
> +				 * during LUN 0 configure, ensures
> +				 * non-responding LUNs are silently skipped;
> +				 * dev->sdev[] is populated by
> +				 * ata_scsi_dev_config() during the scan.
> +				 */
> +				if (dev->class == ATA_DEV_ATAPI &&
> +				    sdev->sdev_bflags & BLIST_FORCELUN) {
> +					dev->nr_luns = ap->scsi_host->max_lun;
> +					scsi_scan_target(
> +						&ap->scsi_host->shost_gendev,
> +						channel, id, SCAN_WILD_CARD,
> +						SCSI_SCAN_RESCAN);
> +				}
>  				scsi_device_put(sdev);
> -			} else {
> -				dev->sdev[0] = NULL;
>  			}
> +
> +			if (dev->sdev[0])
> +				ata_scsi_assign_ofnode(dev, ap);
>  		}
>  	}
>  


-- 
Damien Le Moal
Western Digital Research