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Message-ID: <53e304b4-c025-e884-c8f5-6c2e96cc0052@opensource.wdc.com>
Date:   Thu, 29 Sep 2022 11:22:45 +0900
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Subject: Re: [PATCH 6/6] scsi: mvsas: Use sas_task_find_rq() for tagging
Content-Language: en-US
To:     John Garry <john.garry@huawei.com>, jejb@linux.ibm.com,
        martin.petersen@oracle.com, jinpu.wang@cloud.ionos.com,
        damien.lemoal@wdc.com
Cc:     hare@suse.de, linux-scsi@vger.kernel.org,
        linux-kernel@vger.kernel.org, linuxarm@huawei.com,
        ipylypiv@google.com, changyuanl@google.com, hch@lst.de
References: <1664368034-114991-1-git-send-email-john.garry@huawei.com>
 <1664368034-114991-7-git-send-email-john.garry@huawei.com>
From:   Damien Le Moal <damien.lemoal@opensource.wdc.com>
Organization: Western Digital Research
In-Reply-To: <1664368034-114991-7-git-send-email-john.garry@huawei.com>
Content-Type: text/plain; charset=UTF-8
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Precedence: bulk

On 9/28/22 21:27, 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 slot.
> 
> Unfortunately we don't support reserved commands in the SCSI midlayer yet.
> As such, SMP tasks - as an example - will not have a request associated, so
> in the interim continue to manage those tags for that type of sas_task
> internally.
> 
> We reserve an arbitrary 4 tags for these internal tags. Indeed, we already
> decrement MVS_RSVD_SLOTS by 2 for the shost can_queue when flag
> MVF_FLAG_SOC is set. This change was made in commit 20b09c2992fef
> ("[PATCH] [SCSI] mvsas: add support for 94xx; layout change; bug fixes"),
> but what those 2 slots are used for is not obvious.
> 
> Signed-off-by: John Garry <john.garry@huawei.com>
> ---
>  drivers/scsi/mvsas/mv_defs.h |  1 +
>  drivers/scsi/mvsas/mv_init.c |  4 ++--
>  drivers/scsi/mvsas/mv_sas.c  | 22 +++++++++++++++++-----
>  drivers/scsi/mvsas/mv_sas.h  |  1 -
>  4 files changed, 20 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/scsi/mvsas/mv_defs.h b/drivers/scsi/mvsas/mv_defs.h
> index 7123a2efbf58..8ef174cd4d37 100644
> --- a/drivers/scsi/mvsas/mv_defs.h
> +++ b/drivers/scsi/mvsas/mv_defs.h
> @@ -40,6 +40,7 @@ enum driver_configuration {
>  	MVS_ATA_CMD_SZ		= 96,	/* SATA command table buffer size */
>  	MVS_OAF_SZ		= 64,	/* Open address frame buffer size */
>  	MVS_QUEUE_SIZE		= 64,	/* Support Queue depth */
> +	MVS_RSVD_SLOTS		= 4,
>  	MVS_SOC_CAN_QUEUE	= MVS_SOC_SLOTS - 2,
>  };
>  
> diff --git a/drivers/scsi/mvsas/mv_init.c b/drivers/scsi/mvsas/mv_init.c
> index c85fb812ad43..d834ed9e8e4a 100644
> --- a/drivers/scsi/mvsas/mv_init.c
> +++ b/drivers/scsi/mvsas/mv_init.c
> @@ -284,7 +284,7 @@ static int mvs_alloc(struct mvs_info *mvi, struct Scsi_Host *shost)
>  			printk(KERN_DEBUG "failed to create dma pool %s.\n", pool_name);
>  			goto err_out;
>  	}
> -	mvi->tags_num = slot_nr;
> +	mvi->tags_num = MVS_RSVD_SLOTS;

Same comment as for pm8001: do you really need this field if the value
is always MVS_RSVD_SLOTS ?

>  
>  	return 0;
>  err_out:
> @@ -367,7 +367,7 @@ static struct mvs_info *mvs_pci_alloc(struct pci_dev *pdev,
>  	mvi->sas = sha;
>  	mvi->shost = shost;
>  
> -	mvi->tags = kzalloc(MVS_CHIP_SLOT_SZ>>3, GFP_KERNEL);
> +	mvi->tags = kzalloc(MVS_RSVD_SLOTS, GFP_KERNEL);

Field name ? reserved_tags ?
Also, the alloc seems wrong. This will allocate 4 bytes, but you only
need 4 bits. You could make this an unsigned long and not allocate
anything. Same remark for pm8001 by the way.

That would cap MVS_RSVD_SLOTS to BITS_PER_LONG maximum, but that is easy
to check at compile time with a #if/#error.


>  	if (!mvi->tags)
>  		goto err_out;
>  
> diff --git a/drivers/scsi/mvsas/mv_sas.c b/drivers/scsi/mvsas/mv_sas.c
> index 0810e6c930e1..549d2ec89f60 100644
> --- a/drivers/scsi/mvsas/mv_sas.c
> +++ b/drivers/scsi/mvsas/mv_sas.c
> @@ -20,7 +20,7 @@ static int mvs_find_tag(struct mvs_info *mvi, struct sas_task *task, u32 *tag)
>  	return 0;
>  }
>  
> -void mvs_tag_clear(struct mvs_info *mvi, u32 tag)
> +static void mvs_tag_clear(struct mvs_info *mvi, u32 tag)
>  {
>  	void *bitmap = mvi->tags;
>  	clear_bit(tag, bitmap);
> @@ -28,6 +28,11 @@ void mvs_tag_clear(struct mvs_info *mvi, u32 tag)
>  
>  void mvs_tag_free(struct mvs_info *mvi, u32 tag)
>  {
> +	if (tag < mvi->shost->can_queue)
> +		return;
> +
> +	tag -= mvi->shost->can_queue;
> +
>  	mvs_tag_clear(mvi, tag);
>  }
>  
> @@ -47,6 +52,7 @@ inline int mvs_tag_alloc(struct mvs_info *mvi, u32 *tag_out)
>  	if (tag >= mvi->tags_num)
>  		return -SAS_QUEUE_FULL;
>  	mvs_tag_set(mvi, tag);
> +	tag += mvi->shost->can_queue;
>  	*tag_out = tag;
>  	return 0;
>  }
> @@ -696,6 +702,7 @@ static int mvs_task_prep(struct sas_task *task, struct mvs_info *mvi, int is_tmf
>  	struct mvs_task_exec_info tei;
>  	struct mvs_slot_info *slot;
>  	u32 tag = 0xdeadbeef, n_elem = 0;
> +	struct request *rq;
>  	int rc = 0;
>  
>  	if (!dev->port) {
> @@ -760,9 +767,14 @@ static int mvs_task_prep(struct sas_task *task, struct mvs_info *mvi, int is_tmf
>  		n_elem = task->num_scatter;
>  	}
>  
> -	rc = mvs_tag_alloc(mvi, &tag);
> -	if (rc)
> -		goto err_out;
> +	rq = sas_task_find_rq(task);
> +	if (rq) {
> +		tag = rq->tag;
> +	} else {
> +		rc = mvs_tag_alloc(mvi, &tag);
> +		if (rc)
> +			goto err_out;
> +	}
>  
>  	slot = &mvi->slot_info[tag];
>  
> @@ -857,7 +869,7 @@ int mvs_queue_command(struct sas_task *task, gfp_t gfp_flags)
>  static void mvs_slot_free(struct mvs_info *mvi, u32 rx_desc)
>  {
>  	u32 slot_idx = rx_desc & RXQ_SLOT_MASK;
> -	mvs_tag_clear(mvi, slot_idx);
> +	mvs_tag_free(mvi, slot_idx);
>  }
>  
>  static void mvs_slot_task_free(struct mvs_info *mvi, struct sas_task *task,
> diff --git a/drivers/scsi/mvsas/mv_sas.h b/drivers/scsi/mvsas/mv_sas.h
> index fe57665bdb50..e6c70786ded9 100644
> --- a/drivers/scsi/mvsas/mv_sas.h
> +++ b/drivers/scsi/mvsas/mv_sas.h
> @@ -424,7 +424,6 @@ struct mvs_task_exec_info {
>  
>  /******************** function prototype *********************/
>  void mvs_get_sas_addr(void *buf, u32 buflen);
> -void mvs_tag_clear(struct mvs_info *mvi, u32 tag);
>  void mvs_tag_free(struct mvs_info *mvi, u32 tag);
>  void mvs_tag_set(struct mvs_info *mvi, unsigned int tag);
>  int mvs_tag_alloc(struct mvs_info *mvi, u32 *tag_out);

-- 
Damien Le Moal
Western Digital Research