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

[Vijaya Krishna Nivarthi]

On 4/14/2023 10:12 PM, Doug Anderson wrote:
> Hi,
>
> On Fri, Apr 14, 2023 at 8:48 AM Doug Anderson <dianders@xxxxxxxxxxxx> wrote:
> > Hi,
> >
> > On Fri, Apr 14, 2023 at 7:06 AM Vijaya Krishna Nivarthi
> > <quic_vnivarth@xxxxxxxxxxx> 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