linux-kernel - Re: [PATCH 0/3] ARM: OMAP5+: Support Duty Cycle Correction(DCC)

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Date:	Fri, 23 May 2014 14:07:20 -0700
From:	Mike Turquette <mturquette@...aro.org>
To:	Nishanth Menon <nm@...com>,
	Benoît Cousson <bcousson@...libre.com>,
	"Tony Lindgren" <tony@...mide.com>,
	"Tero Kristo" <t-kristo@...com>, "Paul" <paul@...an.com>
Cc:	"Nishanth Menon" <nm@...com>, devicetree@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-omap@...r.kernel.org
Subject: Re: [PATCH 0/3] ARM: OMAP5+: Support Duty Cycle Correction(DCC)

Quoting Nishanth Menon (2014-05-16 03:45:57)
> Hi,
> 
> This patch series has been carried over in vendor kernel for quiet
> few years now.
> 
> Unfortunately, it was very recently re-discovered and upstream kernel
> is noticed to be broken for OMAP5 1.5GHz - at least we are operating
> DPLL at frequency higher than what it was intended to be when CPUFreq
> is enabled. Thankfully, with nominal voltage(we dont use AVS yet in
> upstream for the mentioned platforms) and margins in trimming, we
> have so far not crashed - but I strongly suspect this might be some
> boundary case survival.

DCC also exists in OMAP4. In some cases customers used it, in other
cases we just ran the PLL way out of spec and the mpu_clk would divide
by 2.

Is this broken for OMAP4 as well?

Regards,
Mike

> 
> Verified on the following impacted platforms using 3.15-rc4 based
> vendor kernel.
> 
> Before:
> OMAP5432: http://slexy.org/view/s20cs0qQFg
> DRA72x: http://slexy.org/view/s2TXtSa6mH (refused to lock)
> DRA75x: http://slexy.org/view/s20AW8MU5c
> After:
> OMAP5432: http://slexy.org/view/s21iAfWxpu
> DRA72x: http://slexy.org/view/s2hwsvGLmC (locks properly)
> DRA75x: http://slexy.org/view/s21ehw8WQn
> 
> Hopefully, we can get these into some kernel revision in some form.
> 
> NOTE: Support for 4470(which is the only other platform requiring
> DCC) is not present in upstream kernel and there are no plans to
> support that SoC, even if it is added at a later point, support can be
> extended as needed.
> 
> Series based on v3.15-rc5 tag.
> Also available on my tree:
>         https://github.com/nmenon/linux-2.6-playground/
>         branch:  push/clock/dcc 
>         
>         weblink: https://github.com/nmenon/linux-2.6-playground/commits/push/clock/dcc
> 
> Verification:
> 3.15-rc4 based kernel - DRA75x-evm, 72x-evm, OMAP5uevm
> 3.15-rc5 - OMAP5uEVM(only one supporting 1.5GHz atm)
> 
> Andrii Tseglytskyi (1):
>   ARM: OMAP5+: dpll: support Duty Cycle Correction(DCC)
> 
> Nishanth Menon (2):
>   clk: dpll: support OMAP5 MPU DPLL that need special handling for
>     higher frequencies
>   ARM: dts: OMAP5/DRA7: use omap5-mpu-dpll-clock capable of dealing
>     with higher frequencies
> 
>  .../devicetree/bindings/clock/ti/dpll.txt          |    1 +
>  arch/arm/boot/dts/dra7xx-clocks.dtsi               |    2 +-
>  arch/arm/boot/dts/omap54xx-clocks.dtsi             |    2 +-
>  arch/arm/mach-omap2/dpll3xxx.c                     |    9 +++++++++
>  drivers/clk/ti/dpll.c                              |   21 ++++++++++++++++++++
>  include/linux/clk/ti.h                             |    4 ++++
>  6 files changed, 37 insertions(+), 2 deletions(-)
> 
> Regards,
> Nishanth Menon
> -- 
> 1.7.9.5
> 
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