[U-Boot] [PATCH] sunxi: improve throughput in the sunxi_mmc driver

[Jagan Teki]

On Wed, Mar 21, 2018 at 4:48 PM, Maxime Ripard
<maxime.ripard at bootlin.com> wrote:
> From: Philipp Tomsich <philipp.tomsich at theobroma-systems.com>
>
> Throughput tests have shown the sunxi_mmc driver to take over 10s to
> read 10MB from a fast eMMC device due to excessive delays in polling
> loops.
>
> This commit restructures the main polling loops to use get_timer(...)
> to determine whether a (millisecond) timeout has expired.  We choose
> not to use the wait_bit function, as we don't need interruptability
> with ctrl-c and have at least one case where two bits (one for an
> error condition and another one for completion) need to be read and
> using wait_bit would have not added to the clarity.
>
> The observed speedup in testing on a A31 is greater than 10x (e.g. a
> 10MB write decreases from 9.302s to 0.884s).

Fyi: I've seen significant improvement, but not 10x on A64
(bananpi-m64) with read

Before this change:

=> mmc dev 0
switch to partitions #0, OK
mmc0 is current device
=> fatload mmc 0:1 $kernel_addr_r Image
reading Image
16310784 bytes read in 821 ms (18.9 MiB/s)
=> mmc dev 1
switch to partitions #0, OK
mmc1(part 0) is current device
=> ext4load mmc 1:1 $kernel_addr_r Image
16310784 bytes read in 1109 ms (14 MiB/s)


After this change:

=> mmc dev 0
switch to partitions #0, OK
mmc0 is current device
=> fatload mmc 0:1 $kernel_addr_r Image
16310784 bytes read in 784 ms (19.8 MiB/s)
=> mmc dev 1
switch to partitions #0, OK
mmc1(part 0) is current device
=> ext4load mmc 1:1 $kernel_addr_r Image
16310784 bytes read in 793 ms (19.6 MiB/s)

Jagan.