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Subject: Re: [PATCH] NCR5380: Support chained sg lists
To:     Finn Thain <fthain@telegraphics.com.au>,
        "James E.J. Bottomley" <jejb@linux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>
Cc:     linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org
References: <739c214bafcb9af3f6d5037cc03f57f692966675.1560223509.git.fthain@telegraphics.com.au>
From:   Michael Schmitz <schmitzmic@gmail.com>
Message-ID: <a79e01ba-e47c-6b29-3625-29bfb7122ad8@gmail.com>
Date:   Wed, 12 Jun 2019 11:47:56 +1200
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On 11/06/19 3:25 PM, Finn Thain wrote:

> My understanding is that support for chained scatterlists is to
> become mandatory for LLDs.
>
> Cc: Michael Schmitz <schmitzmic@gmail.com>
> Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Reviewed-by: Michael Schmitz <schmitzmic@gmail.com>
> ---
>   drivers/scsi/NCR5380.c | 41 ++++++++++++++++++-----------------------
>   1 file changed, 18 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/scsi/NCR5380.c b/drivers/scsi/NCR5380.c
> index d9fa9cf2fd8b..536426f25e86 100644
> --- a/drivers/scsi/NCR5380.c
> +++ b/drivers/scsi/NCR5380.c
> @@ -149,12 +149,10 @@ static inline void initialize_SCp(struct scsi_cmnd *cmd)
>   
>   	if (scsi_bufflen(cmd)) {
>   		cmd->SCp.buffer = scsi_sglist(cmd);
> -		cmd->SCp.buffers_residual = scsi_sg_count(cmd) - 1;
>   		cmd->SCp.ptr = sg_virt(cmd->SCp.buffer);
>   		cmd->SCp.this_residual = cmd->SCp.buffer->length;
>   	} else {
>   		cmd->SCp.buffer = NULL;
> -		cmd->SCp.buffers_residual = 0;
>   		cmd->SCp.ptr = NULL;
>   		cmd->SCp.this_residual = 0;
>   	}
> @@ -163,6 +161,17 @@ static inline void initialize_SCp(struct scsi_cmnd *cmd)
>   	cmd->SCp.Message = 0;
>   }
>   
> +static inline void advance_sg_buffer(struct scsi_cmnd *cmd)
> +{
> +	struct scatterlist *s = cmd->SCp.buffer;
> +
> +	if (!cmd->SCp.this_residual && s && !sg_is_last(s)) {
> +		cmd->SCp.buffer = sg_next(s);
> +		cmd->SCp.ptr = sg_virt(cmd->SCp.buffer);
> +		cmd->SCp.this_residual = cmd->SCp.buffer->length;
> +	}
> +}
> +
>   /**
>    * NCR5380_poll_politely2 - wait for two chip register values
>    * @hostdata: host private data
> @@ -1670,12 +1679,7 @@ static void NCR5380_information_transfer(struct Scsi_Host *instance)
>   			    sun3_dma_setup_done != cmd) {
>   				int count;
>   
> -				if (!cmd->SCp.this_residual && cmd->SCp.buffers_residual) {
> -					++cmd->SCp.buffer;
> -					--cmd->SCp.buffers_residual;
> -					cmd->SCp.this_residual = cmd->SCp.buffer->length;
> -					cmd->SCp.ptr = sg_virt(cmd->SCp.buffer);
> -				}
> +				advance_sg_buffer(cmd);
>   
>   				count = sun3scsi_dma_xfer_len(hostdata, cmd);
>   
> @@ -1725,15 +1729,11 @@ static void NCR5380_information_transfer(struct Scsi_Host *instance)
>   				 * scatter-gather list, move onto the next one.
>   				 */
>   
> -				if (!cmd->SCp.this_residual && cmd->SCp.buffers_residual) {
> -					++cmd->SCp.buffer;
> -					--cmd->SCp.buffers_residual;
> -					cmd->SCp.this_residual = cmd->SCp.buffer->length;
> -					cmd->SCp.ptr = sg_virt(cmd->SCp.buffer);
> -					dsprintk(NDEBUG_INFORMATION, instance, "%d bytes and %d buffers left\n",
> -					         cmd->SCp.this_residual,
> -					         cmd->SCp.buffers_residual);
> -				}
> +				advance_sg_buffer(cmd);
> +				dsprintk(NDEBUG_INFORMATION, instance,
> +					"this residual %d, sg ents %d\n",
> +					cmd->SCp.this_residual,
> +					sg_nents(cmd->SCp.buffer));
>   
>   				/*
>   				 * The preferred transfer method is going to be
> @@ -2126,12 +2126,7 @@ static void NCR5380_reselect(struct Scsi_Host *instance)
>   	if (sun3_dma_setup_done != tmp) {
>   		int count;
>   
> -		if (!tmp->SCp.this_residual && tmp->SCp.buffers_residual) {
> -			++tmp->SCp.buffer;
> -			--tmp->SCp.buffers_residual;
> -			tmp->SCp.this_residual = tmp->SCp.buffer->length;
> -			tmp->SCp.ptr = sg_virt(tmp->SCp.buffer);
> -		}
> +		advance_sg_buffer(tmp);
>   
>   		count = sun3scsi_dma_xfer_len(hostdata, tmp);
>