linux-kernel - Re: [PATCH v3 0/3] spi: Add DMA mode support to spi-qcom-qspi

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Date:   Fri, 14 Apr 2023 08:48:46 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
Cc:     agross@...nel.org, andersson@...nel.org, konrad.dybcio@...aro.org,
        broonie@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org,
        cros-qcom-dts-watchers@...omium.org, linux-arm-msm@...r.kernel.org,
        linux-spi@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, quic_msavaliy@...cinc.com,
        mka@...omium.org, swboyd@...omium.org, quic_vtanuku@...cinc.com
Subject: Re: [PATCH v3 0/3] spi: Add DMA mode support to spi-qcom-qspi

Hi,

On Fri, Apr 14, 2023 at 7:06 AM Vijaya Krishna Nivarthi
<quic_vnivarth@...cinc.com> wrote:
>
> There are large number of QSPI irqs that fire during boot/init and later
> on every suspend/resume.
> This could be made faster by doing DMA instead of PIO.
> Below is comparison for number of interrupts raised in 2 acenarios...

s/acenarios/scenarios

> Boot up and stabilise
> Suspend/Resume
>
> Sequence   PIO    DMA
> =======================
> Boot-up    69088  19284
> S/R        5066   3430
>
> Though we have not made measurements for speed, power we expect
> the performance to be better with DMA mode and no regressions were
> encountered in testing.

Measuring the speed isn't really very hard, so I gave it a shot.

I used a truly terrible python script to do this on a Chromebook:

--

import os
import time

os.system("""
stop ui
stop powerd

cd /sys/devices/system/cpu/cpufreq
for policy in policy*; do
  cat ${policy}/cpuinfo_max_freq > ${policy}/scaling_min_freq
done
""")

all_times = []
for i in range(1000):
  start = time.time()
  os.system("flashrom -p host -r /tmp/foo.bin")
  end = time.time()

  all_times.append(end - start)
  print("Iteration %d, min=%.2f, max=%.2f, avg=%.2f" % (
      i, min(all_times), max(all_times), sum(all_times) / len(all_times)))

--

The good news is that after applying your patches the loop runs _much_ faster.

The bad news is that it runs much faster because it very quickly fails
and errors out. flashrom just keeps reporting:

Opened /dev/mtd0 successfully
Found Programmer flash chip "Opaque flash chip" (8192 kB,
Programmer-specific) on host.
Reading flash... Cannot read 0x001000 bytes at 0x000000: Connection timed out
read_flash: failed to read (00000000..0x7fffff).
Read operation failed!
FAILED.
FAILED

I went back and tried v1, v2, and v3 and all three versions fail.