linux-kernel - Re: [PATCH v2 4/6] scsi: pm8001: Use sas_task_find

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Date:   Tue, 4 Oct 2022 07:53:10 +0200
From:   Hannes Reinecke <hare@...e.de>
To:     John Garry <john.garry@...wei.com>, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, jinpu.wang@...ud.ionos.com,
        damien.lemoal@....com
Cc:     linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxarm@...wei.com, ipylypiv@...gle.com, changyuanl@...gle.com,
        hch@....de, yanaijie@...wei.com
Subject: Re: [PATCH v2 4/6] scsi: pm8001: Use sas_task_find_rq() for tagging

On 9/30/22 10:56, John Garry wrote:
> The request associated with a scsi command coming from the block layer
> has a unique tag, so use that when possible for getting a CCB.
> 
> Unfortunately we don't support reserved commands in the SCSI midlayer yet,
> so in the interim continue to manage those tags internally (along with
> tags for private commands).
> 
> Signed-off-by: John Garry <john.garry@...wei.com>
> ---
>   drivers/scsi/pm8001/pm8001_init.c | 12 ++++--------
>   drivers/scsi/pm8001/pm8001_sas.c  | 16 ++++++++++++----
>   drivers/scsi/pm8001/pm8001_sas.h  | 11 ++++++++---
>   drivers/scsi/pm8001/pm80xx_hwi.c  | 17 +++--------------
>   4 files changed, 27 insertions(+), 29 deletions(-)
> 
> diff --git a/drivers/scsi/pm8001/pm8001_init.c b/drivers/scsi/pm8001/pm8001_init.c
> index 0edc9857a8bd..abb884ddcaf9 100644
> --- a/drivers/scsi/pm8001/pm8001_init.c
> +++ b/drivers/scsi/pm8001/pm8001_init.c
> @@ -196,7 +196,7 @@ static void pm8001_free(struct pm8001_hba_info *pm8001_ha)
>   	}
>   	PM8001_CHIP_DISP->chip_iounmap(pm8001_ha);
>   	flush_workqueue(pm8001_wq);
> -	bitmap_free(pm8001_ha->tags);
> +	bitmap_free(pm8001_ha->rsvd_tags);
>   	kfree(pm8001_ha);
>   }
>   
> @@ -1208,18 +1208,15 @@ static int pm8001_init_ccb_tag(struct pm8001_hba_info *pm8001_ha)
>   	struct Scsi_Host *shost = pm8001_ha->shost;
>   	struct device *dev = pm8001_ha->dev;
>   	u32 max_out_io, ccb_count;
> -	u32 can_queue;
>   	int i;
>   
>   	max_out_io = pm8001_ha->main_cfg_tbl.pm80xx_tbl.max_out_io;
>   	ccb_count = min_t(int, PM8001_MAX_CCB, max_out_io);
>   
> -	/* Update to the scsi host*/
> -	can_queue = ccb_count - PM8001_RESERVE_SLOT;
> -	shost->can_queue = can_queue;
> +	shost->can_queue = ccb_count - PM8001_RESERVE_SLOT;
>   
> -	pm8001_ha->tags = bitmap_zalloc(ccb_count, GFP_KERNEL);
> -	if (!pm8001_ha->tags)
> +	pm8001_ha->rsvd_tags = bitmap_zalloc(PM8001_RESERVE_SLOT, GFP_KERNEL);
> +	if (!pm8001_ha->rsvd_tags)
>   		goto err_out;
>   
>   	/* Memory region for ccb_info*/
> @@ -1244,7 +1241,6 @@ static int pm8001_init_ccb_tag(struct pm8001_hba_info *pm8001_ha)
>   		pm8001_ha->ccb_info[i].task = NULL;
>   		pm8001_ha->ccb_info[i].ccb_tag = PM8001_INVALID_TAG;
>   		pm8001_ha->ccb_info[i].device = NULL;
> -		++pm8001_ha->tags_num;
>   	}
>   
>   	return 0;
> diff --git a/drivers/scsi/pm8001/pm8001_sas.c b/drivers/scsi/pm8001/pm8001_sas.c
> index 066dfa9f4683..d60bc311a4e9 100644
> --- a/drivers/scsi/pm8001/pm8001_sas.c
> +++ b/drivers/scsi/pm8001/pm8001_sas.c
> @@ -65,9 +65,14 @@ static int pm8001_find_tag(struct sas_task *task, u32 *tag)
>     */
>   void pm8001_tag_free(struct pm8001_hba_info *pm8001_ha, u32 tag)
>   {
> -	void *bitmap = pm8001_ha->tags;
> +	void *bitmap = pm8001_ha->rsvd_tags;
>   	unsigned long flags;
>   
> +	if (tag < pm8001_ha->shost->can_queue)
> +		return;
> +
> +	tag -= pm8001_ha->shost->can_queue;
> +
>   	spin_lock_irqsave(&pm8001_ha->bitmap_lock, flags);
>   	__clear_bit(tag, bitmap);
>   	spin_unlock_irqrestore(&pm8001_ha->bitmap_lock, flags);
> @@ -80,18 +85,21 @@ void pm8001_tag_free(struct pm8001_hba_info *pm8001_ha, u32 tag)
>     */
>   int pm8001_tag_alloc(struct pm8001_hba_info *pm8001_ha, u32 *tag_out)
>   {
> -	void *bitmap = pm8001_ha->tags;
> +	void *bitmap = pm8001_ha->rsvd_tags;
>   	unsigned long flags;
>   	unsigned int tag;
>   
>   	spin_lock_irqsave(&pm8001_ha->bitmap_lock, flags);
> -	tag = find_first_zero_bit(bitmap, pm8001_ha->tags_num);
> -	if (tag >= pm8001_ha->tags_num) {
> +	tag = find_first_zero_bit(bitmap, PM8001_RESERVE_SLOT);
> +	if (tag >= PM8001_RESERVE_SLOT) {
>   		spin_unlock_irqrestore(&pm8001_ha->bitmap_lock, flags);
>   		return -SAS_QUEUE_FULL;
>   	}
>   	__set_bit(tag, bitmap);
>   	spin_unlock_irqrestore(&pm8001_ha->bitmap_lock, flags);
> +
> +	/* reserved tags are in the upper region of the tagset */
> +	tag += pm8001_ha->shost->can_queue;
>   	*tag_out = tag;
>   	return 0;
>   }
Can you move the reserved tags to the _lower_ region of the tagset?
That way the tag allocation scheme matches with what the block-layer 
does, and the eventual conversion to reserved tags becomes easier.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@...e.de                              +49 911 74053 688
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