On 21/11/2014 13:41, 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@xxxxxxx>
> ---
> 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 86c4c42..1c1312f 100644
> --- a/drivers/scsi/am53c974.c
> +++ b/drivers/scsi/am53c974.c
> @@ -197,6 +197,12 @@ 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_ONCE(resid == 1)) {
> + 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 2a3277d..07b4d93 100644
> --- a/drivers/scsi/esp_scsi.c
> +++ b/drivers/scsi/esp_scsi.c
> @@ -1334,6 +1334,35 @@ 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];
>
Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
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