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SubjectRe: [PATCH v2 77/71] ncr5380: Fix wait for 53C80 registers registers after PDMA

On Mon, 7 Dec 2015, Ondrej Zary wrote:

> The check for 53C80 registers accessibility was commented out because
> it was broken (inverted). Fix and enable it.
>
> Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
> ---
> drivers/scsi/g_NCR5380.c | 37 ++++++-------------------------------
> 1 file changed, 6 insertions(+), 31 deletions(-)
>
> diff --git a/drivers/scsi/g_NCR5380.c b/drivers/scsi/g_NCR5380.c
> index 038dddf..a7479c6 100644
> --- a/drivers/scsi/g_NCR5380.c
> +++ b/drivers/scsi/g_NCR5380.c
> @@ -603,14 +603,10 @@ static inline int NCR5380_pread(struct Scsi_Host *instance, unsigned char *dst,
> if (!(NCR5380_read(hostdata->c400_ctl_status) & CSR_GATED_53C80_IRQ))
> printk("53C400r: no 53C80 gated irq after transfer");
>
> -#if 0
> - /*
> - * DON'T DO THIS - THEY NEVER ARRIVE!
> - */
> - printk("53C400r: Waiting for 53C80 registers\n");
> - while (NCR5380_read(hostdata->c400_ctl_status) & CSR_53C80_REG)
> + /* wait for 53C80 registers to be available */
> + while (!(NCR5380_read(hostdata->c400_ctl_status) & CSR_53C80_REG))
> ;

In the previous patch, udelay(4) was added to a CSR_GATED_53C80_IRQ
polling loop. It is interesting that you don't need it here when polling
CSR_53C80_REG.

> -#endif
> +
> if (!(NCR5380_read(BUS_AND_STATUS_REG) & BASR_END_DMA_TRANSFER))
> printk(KERN_ERR "53C400r: no end dma signal\n");
>
> @@ -632,7 +628,6 @@ static inline int NCR5380_pwrite(struct Scsi_Host *instance, unsigned char *src,
> struct NCR5380_hostdata *hostdata = shost_priv(instance);
> int blocks = len / 128;
> int start = 0;
> - int i;
>
> NCR5380_write(hostdata->c400_ctl_status, CSR_BASE);
> NCR5380_write(hostdata->c400_blk_cnt, blocks);
> @@ -681,36 +676,16 @@ static inline int NCR5380_pwrite(struct Scsi_Host *instance, unsigned char *src,
> blocks--;
> }
>
> -#if 0
> - printk("53C400w: waiting for registers to be available\n");
> - THEY NEVER DO ! while (NCR5380_read(hostdata->c400_ctl_status) & CSR_53C80_REG);
> - printk("53C400w: Got em\n");
> -#endif
> -
> - /* Let's wait for this instead - could be ugly */
> - /* All documentation says to check for this. Maybe my hardware is too
> - * fast. Waiting for it seems to work fine! KLL
> - */
> - while (!(i = NCR5380_read(hostdata->c400_ctl_status) & CSR_GATED_53C80_IRQ)) {
> + /* wait for 53C80 registers to be available */
> + while (!(NCR5380_read(hostdata->c400_ctl_status) & CSR_53C80_REG)) {
> udelay(4); /* DTC436 chip hangs without this */

... based on the above, this udelay is probably not needed.

(Or perhaps it is only needed once, in between the final host_buf register
access and the first ctl_status access??)

Is there any reference in the docs to timing sensitivity?

> /* FIXME - no timeout */
> }
>
> - /*
> - * I know. i is certainly != 0 here but the loop is new. See previous
> - * comment.
> - */

Thanks for cleaning up this mess!

--

> - if (i) {
> - if (!((i = NCR5380_read(BUS_AND_STATUS_REG)) & BASR_END_DMA_TRANSFER))
> - printk(KERN_ERR "53C400w: No END OF DMA bit - WHOOPS! BASR=%0x\n", i);
> - } else
> - printk(KERN_ERR "53C400w: no 53C80 gated irq after transfer (last block)\n");
> -
> -#if 0
> if (!(NCR5380_read(BUS_AND_STATUS_REG) & BASR_END_DMA_TRANSFER)) {
> printk(KERN_ERR "53C400w: no end dma signal\n");
> }
> -#endif
> +
> while (!(NCR5380_read(TARGET_COMMAND_REG) & TCR_LAST_BYTE_SENT))
> ; // TIMEOUT
> return 0;
>


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