Re: [PATCH v4 4/8] ARM: Exynos: use generic cpufreq driver for Exynos5420

[Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>]

Hi,

On Tuesday, December 08, 2015 04:36:12 PM Krzysztof Kozlowski wrote:
> On 08.12.2015 03:18, Bartlomiej Zolnierkiewicz wrote:
> > From: Thomas Abraham <thomas.ab@samsung.com>
> > 
> > The new CPU clock type allows the use of cpufreq-dt driver
> > for Exynos5420.
> > 
> > Changes by Bartlomiej:
> > - split Exynos5420 support from the original patch
> > - disable cpufreq if big.LITTLE switcher support is enabled
> > - switch to using cpufreq-dt driver
> > 
> > Cc: Tomasz Figa <tomasz.figa@gmail.com>
> > Cc: Kukjin Kim <kgene.kim@samsung.com>
> > Cc: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
> > Signed-off-by: Thomas Abraham <thomas.ab@samsung.com>
> > Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
> > ---
> >  arch/arm/mach-exynos/exynos.c | 3 +++
> >  1 file changed, 3 insertions(+)
> 
> I think this is actually now your patch, not Thomas any more. :)

It seems so, I'll update the patch.

> > diff --git a/arch/arm/mach-exynos/exynos.c b/arch/arm/mach-exynos/exynos.c
> > index 1c47aee..7a89c9d 100644
> > --- a/arch/arm/mach-exynos/exynos.c
> > +++ b/arch/arm/mach-exynos/exynos.c
> > @@ -230,6 +230,9 @@ static const struct of_device_id exynos_cpufreq_matches[] = {
> >  	{ .compatible = "samsung,exynos4212", .data = "cpufreq-dt" },
> >  	{ .compatible = "samsung,exynos4412", .data = "cpufreq-dt" },
> >  	{ .compatible = "samsung,exynos5250", .data = "cpufreq-dt" },
> > +#ifndef CONFIG_BL_SWITCHER
> > +	{ .compatible = "samsung,exynos5420", .data = "cpufreq-dt" },
> > +#endif
> 
> Why not on BL_SWITCHER? Shouldn't be enough to disable ARM_DT_BL_CPUFREQ?

ARM_DT_BL_CPUFREQ is not relevant here (it requires to be explicitly
enabled by platform code, just like cpufreq-dt) and the dependency on
!BL_SWITCHER is needed because when BL_SWITCHER is enabled big and
LITTLE cores are grouped in pairs and presented as "virtual" CPUs to
the system:

...
[    0.002630] CPU0: update cpu_capacity 448
[    0.002646] CPU0: thread -1, cpu 0, socket 1, mpidr 80000100
[    0.002835] Setting up static identity map for 0x40008280 - 0x400082d8
[    0.003106] ARM CCI driver probed
[    0.003351] Exynos MCPM support installed
[    0.045350] CPU1: update cpu_capacity 448
[    0.045358] CPU1: thread -1, cpu 1, socket 1, mpidr 80000101
[    0.060326] CPU2: update cpu_capacity 448
[    0.060334] CPU2: thread -1, cpu 2, socket 1, mpidr 80000102
[    0.075326] CPU3: update cpu_capacity 448
[    0.075334] CPU3: thread -1, cpu 3, socket 1, mpidr 80000103
[    0.090337] CPU4: update cpu_capacity 1535
[    0.090345] CPU4: thread -1, cpu 0, socket 0, mpidr 80000000
[    0.105314] CPU5: update cpu_capacity 1535
[    0.105321] CPU5: thread -1, cpu 1, socket 0, mpidr 80000001
[    0.120338] CPU6: update cpu_capacity 1535
[    0.120345] CPU6: thread -1, cpu 2, socket 0, mpidr 80000002
[    0.135330] CPU7: update cpu_capacity 1535
[    0.135338] CPU7: thread -1, cpu 3, socket 0, mpidr 80000003
[    0.135466] Brought up 8 CPUs
...
[    3.027498] big.LITTLE switcher initializing
[    3.031761] CPU0 paired with CPU7
[    3.035055] CPU1 paired with CPU6
[    3.038332] CPU2 paired with CPU5
[    3.041598] CPU3 paired with CPU4
[    3.044930] GIC ID for CPU 0 cluster 1 is 4
[    3.049078] GIC ID for CPU 1 cluster 1 is 5
[    3.053258] GIC ID for CPU 2 cluster 1 is 6
[    3.057370] GIC ID for CPU 3 cluster 1 is 7
[    3.061558] GIC ID for CPU 0 cluster 0 is 0
[    3.083336] IRQ53 no longer affine to CPU4
[    3.084336] CPU4: shutdown
[    3.107059] GIC ID for CPU 1 cluster 0 is 1
[    3.123303] IRQ54 no longer affine to CPU5
[    3.124213] CPU5: shutdown
[    3.146387] GIC ID for CPU 2 cluster 0 is 2
[    3.158143] cpu cpu0: 1100 MHz, 1250 mV --> 900 MHz, 1100 mV
[    3.168228] IRQ55 no longer affine to CPU6
[    3.169135] CPU6: shutdown
[    3.191485] GIC ID for CPU 3 cluster 0 is 3
[    3.208264] IRQ56 no longer affine to CPU7
[    3.209166] CPU7: shutdown
[    3.236752] big.LITTLE switcher initialized
...

Only arm_big_little_dt driver knows how to handle this setup
correctly.  cpufreq-dt just treats "virtual" CPUs as a LITTLE
ones.  Thus when "virtual CPU"'s current core is switched to
a big one cpufreq-dt is unable to update its voltage.

[ I tried using BL_SWITCHER_DUMMY_IF functionality to simulate
  this with:

	echo 0,0 > /dev/b.L_switcher

  but it doesn't seem to work for some reason (from looking at
  arch/arm/common/bL_switcher_dummy_if.c code it seems that at
  least "bL_switcher_write" line should get logged but it does
  not happen). ]

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics