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 22:31:00 +0530
From:   Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
To:     Doug Anderson <dianders@...omium.org>
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

On 4/14/2023 10:12 PM, Doug Anderson wrote:
> 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.


Thank you very much for the review, script, test and quick debug.
Will check same and update a v4.

-Vijay/


> -Doug