linux-kernel - Re: [PATCH v2 1/4] ARM: davinci: fix cpufreq registration on da850-evm

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Message-ID: <CAMRc=MdYhaED30Xu8oJiJD7F9z=SPu6u+1p32mQnX0tEL=iOiA@mail.gmail.com>
Date:   Wed, 3 Apr 2019 14:50:23 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Sekhar Nori <nsekhar@...com>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Adam Ford <aford173@...il.com>,
        Kevin Hilman <khilman@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        David Lechner <david@...hnology.com>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        arm-soc <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 1/4] ARM: davinci: fix cpufreq registration on da850-evm

śr., 27 mar 2019 o 12:14 Sekhar Nori <nsekhar@...com> napisał(a):
>
> Hi Bart,
>
> On 26/03/19 11:21 PM, Bartosz Golaszewski wrote:
> > wt., 26 mar 2019 o 15:00 Adam Ford <aford173@...il.com> napisał(a):
> >>
> >> On Fri, Mar 22, 2019 at 8:31 AM Bartosz Golaszewski <brgl@...ev.pl> wrote:
> >>>
> >>> From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> >>>
> >>> The system_rev variable is never set on davinci and is always 0, so
> >>> we're using the default max operating point of 300MHz. The cvdd supply
> >>> comes from the tps6507 pmic and the voltage can go all the way to 1.3V
> >>> so the maximum supported rate should be 456MHz.
> >>
> >> My understanding is that only certain revisions of the silicon can go
> >> to 456MHz.   The L138's Datasheet lists both a 456 and 375 version.  I
> >> cannot find a way to read a register to determine which version of the
> >> silicon is available. Maybe Sekhar can confirm.
> >>
> >
> > Commit 28bd2c341120 ("davinci: am18x/da850/omap-l138 evm: add support
> > for higher speed grades") mentions the following:
> >
> > ---
> > U-Boot on the EVM sets up ATAG_REVISION to inform the OS
> > regarding the speed grade supported by the silicon. We use
> > this information to pass on the speed grade information to
> > the SoC code.
> > ---
> >
> > Should the system_rev somehow reflect that revision? Any way I can check it?
>
> Can you check if the procedure in doc/README.davinci in U-Boot sources
> still works?
>
> Environment Variables
> =====================
>
> The DA850 EVM allows the user to specify the maximum cpu clock allowed by the
> silicon, in Hz, via an environment variable "maxcpuclk".
>
> The maximum clock rate allowed depends on the silicon populated on the EVM.
> Please make sure you understand the restrictions placed on this clock in the
> device specific datasheet before setting up this variable. This information is
> passed to the Linux kernel using the ATAG_REVISION atag.
>
> If "maxcpuclk" is not defined, the configuration CONFIG_DA850_EVM_MAX_CPU_CLK
> is used to obtain this information.
>
> Thanks,
> Sekhar

Hi Sekhar,

I built the current upstream u-boot and the get_board_rev() function
for da850-evm doesn't seem to be called at all. For instance the
lego-ev3 platform does this:

./lego/ev3/legoev3.c:108: board_rev = get_board_rev();

but in davinci this function seems to be unused and I don't see it
called from any other core u-boot component. I don't see any commit
that would mention this function but there are a lot of commits
removing get_board_rev() for other boards in git log. Is it possible
it stopped being used at some point?

Bart