On Wed, 2021-07-21 at 20:34 -0700, Bart Van Assche wrote:

Using the UTRLCNR register involves two MMIO accesses in the hot path
while
using the doorbell register only involves a single MMIO access. Since
MMIO
accesses take time, do not use the UTRLCNR register. The spinlock
contention
on the SCSI host lock that is reintroduced by this patch will be
addressed
by a later patch.

This reverts commit 6f7151729647e58ac7c522081255fd0c07b38105.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Stanley Chu <redacted>
Cc: Can Guo <redacted>
Cc: Asutosh Das <redacted>
Cc: Avri Altman <avri.altman@wdc.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>

Hi Bart, 

I did the comparison test on my platform, it is very difficult to get a
very clear and fair result between two changes. but lamely speaking, on
the small chunk size read/write, your changes wins. but on the big
chunk size, It is not very clear, the gap between the two changes can
be ignored.

Tested-by: Bean Huo <redacted>

Bean