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 09:42:00 -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 8:48 AM Doug Anderson <dianders@...omium.org> wrote:
>
> 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.

Ah, I see what's likely the problem. Your patch series only adds the
"iommus" for sc7280 but I'm testing on sc7180. That means:

1. You need to add the iommus to _all_ the boards that have qspi. That
means sc7280, sc7180, and sdm845.

2. Ideally the code should still be made to work (it should fall back
to PIO mode) if DMA isn't properly enabled. That would keep old device
trees working, which we're supposed to do.

-Doug