Re: [PATCH 08/10] am53c974: BLAST residual handling

[Paolo Bonzini <pbonzini@redhat.com>]

On 21/11/2014 10:27, Hannes Reinecke wrote:
> The am53c974 has an design issue where a single byte might be
> left in the SCSI FIFO after a DMA transfer.
> As the handling code is currently untested add a WARN_ON()
> statement here.
> 
> Signed-off-by: Hannes Reinecke <hare@suse.de>
> ---
>  drivers/scsi/am53c974.c |  6 ++++++
>  drivers/scsi/esp_scsi.c | 29 +++++++++++++++++++++++++++++
>  drivers/scsi/esp_scsi.h |  1 +
>  3 files changed, 36 insertions(+)
> 
> diff --git a/drivers/scsi/am53c974.c b/drivers/scsi/am53c974.c
> index 652762e..0b7643e 100644
> --- a/drivers/scsi/am53c974.c
> +++ b/drivers/scsi/am53c974.c
> @@ -195,6 +195,12 @@ static void pci_esp_dma_drain(struct esp *esp)
>  	shost_printk(KERN_INFO, esp->host,
>  		     "DMA blast done (%d tries, %d bytes left)\n", lim, resid);
>  #endif
> +	/* BLAST residual handling is currently untested */
> +	if (WARN_ON(resid == 1)) {

WARN_ON_ONCE?

Paolo

> +		struct esp_cmd_entry *ent = esp->active_cmd;
> +
> +		ent->flags |= ESP_CMD_FLAG_RESIDUAL;
> +	}
>  }
>  
>  static void pci_esp_dma_invalidate(struct esp *esp)
> diff --git a/drivers/scsi/esp_scsi.c b/drivers/scsi/esp_scsi.c
> index ab7d2bc..88272bb 100644
> --- a/drivers/scsi/esp_scsi.c
> +++ b/drivers/scsi/esp_scsi.c
> @@ -1353,6 +1353,35 @@ static int esp_data_bytes_sent(struct esp *esp, struct esp_cmd_entry *ent,
>  	bytes_sent = esp->data_dma_len;
>  	bytes_sent -= ecount;
>  
> +	/*
> +	 * The am53c974 has a DMA 'pecularity'. The doc states:
> +	 * In some odd byte conditions, one residual byte will
> +	 * be left in the SCSI FIFO, and the FIFO Flags will
> +	 * never count to '0 '. When this happens, the residual
> +	 * byte should be retrieved via PIO following completion
> +	 * of the BLAST operation.
> +	 */
> +	if (fifo_cnt == 1 && ent->flags & ESP_CMD_FLAG_RESIDUAL) {
> +		size_t count = 1;
> +		size_t offset = bytes_sent;
> +		u8 bval = esp_read8(ESP_FDATA);
> +
> +		if (ent->flags & ESP_CMD_FLAG_AUTOSENSE)
> +			ent->sense_ptr[bytes_sent] = bval;
> +		else {
> +			struct esp_cmd_priv *p = ESP_CMD_PRIV(cmd);
> +			u8 *ptr;
> +
> +			ptr = scsi_kmap_atomic_sg(p->cur_sg, p->u.num_sg,
> +						  &offset, &count);
> +			if (likely(ptr)) {
> +				*(ptr + offset) = bval;
> +				scsi_kunmap_atomic_sg(ptr);
> +			}
> +		}
> +		bytes_sent += fifo_cnt;
> +		ent->flags &= ~ESP_CMD_FLAG_RESIDUAL;
> +	}
>  	if (!(ent->flags & ESP_CMD_FLAG_WRITE))
>  		bytes_sent -= fifo_cnt;
>  
> diff --git a/drivers/scsi/esp_scsi.h b/drivers/scsi/esp_scsi.h
> index 27dcaf8..5fa456c 100644
> --- a/drivers/scsi/esp_scsi.h
> +++ b/drivers/scsi/esp_scsi.h
> @@ -269,6 +269,7 @@ struct esp_cmd_entry {
>  #define ESP_CMD_FLAG_WRITE	0x01 /* DMA is a write */
>  #define ESP_CMD_FLAG_ABORT	0x02 /* being aborted */
>  #define ESP_CMD_FLAG_AUTOSENSE	0x04 /* Doing automatic REQUEST_SENSE */
> +#define ESP_CMD_FLAG_RESIDUAL	0x08 /* AM53c974 BLAST residual */
>  
>  	u8			tag[2];
>  	u8			orig_tag[2];
>