Re: [PATCH v2 1/4] ARM: davinci: fix cpufreq registration on da850-evm
From: Bartosz Golaszewski
Date: Wed Apr 03 2019 - 08:50:38 EST
År., 27 mar 2019 o 12:14 Sekhar Nori <nsekhar@xxxxxx> napisaÅ(a):
> Hi Bart,
> On 26/03/19 11:21 PM, Bartosz Golaszewski wrote:
> > wt., 26 mar 2019 o 15:00 Adam Ford <aford173@xxxxxxxxx> napisaÅ(a):
> >> On Fri, Mar 22, 2019 at 8:31 AM Bartosz Golaszewski <brgl@xxxxxxxx> wrote:
> >>> From: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
> >>> 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.
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?