netdev - Re: [PATCH v11 4/5] powerpc: Add flexcan device support for p1010rdb.

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Date:	Wed, 10 Aug 2011 23:46:27 -0500
From:	Kumar Gala <galak@...nel.crashing.org>
To:	Wolfgang Grandegger <wg@...ndegger.com>
Cc:	Robin Holt <holt@....com>, netdev@...r.kernel.org,
	U Bhaskar-B22300 <B22300@...escale.com>,
	socketcan-core@...ts.berlios.de,
	Marc Kleine-Budde <mkl@...gutronix.de>,
	PPC list <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v11 4/5] powerpc: Add flexcan device support for p1010rdb.


On Aug 10, 2011, at 1:16 PM, Wolfgang Grandegger wrote:

> On 08/10/2011 07:01 PM, Kumar Gala wrote:
>> 
>> On Aug 10, 2011, at 11:27 AM, Robin Holt wrote:
>> 
>>> I added a simple clock source for the p1010rdb so the flexcan driver
>>> could determine a clock frequency.  The p1010 flexcan device only has
>>> an oscillator of system bus frequency divided by 2.
>>> 
>>> Signed-off-by: Robin Holt <holt@....com>
>>> Acked-by: Marc Kleine-Budde <mkl@...gutronix.de>,
>>> Acked-by: Wolfgang Grandegger <wg@...ndegger.com>,
>>> Cc: U Bhaskar-B22300 <B22300@...escale.com>
>>> Cc: socketcan-core@...ts.berlios.de,
>>> Cc: netdev@...r.kernel.org,
>>> Cc: PPC list <linuxppc-dev@...ts.ozlabs.org>
>>> Cc: Kumar Gala <galak@...nel.crashing.org>
>>> ---
>>> arch/powerpc/platforms/85xx/Kconfig    |    2 +
>>> arch/powerpc/platforms/85xx/Makefile   |    2 +
>>> arch/powerpc/platforms/85xx/clock.c    |   52 ++++++++++++++++++++++++++++++++
>>> arch/powerpc/platforms/85xx/p1010rdb.c |    8 +++++
>>> 4 files changed, 64 insertions(+), 0 deletions(-)
>>> create mode 100644 arch/powerpc/platforms/85xx/clock.c
>> 
>> I dont understand how mpc85xx_clk_functions() ends up being associated with the frequency the flexcan is running at.
> 
> The function mpc85xx_clk_get_rate() returns "fsl_get_sys_freq() / 2" for
> Flexcan devices.
> 
>> This either seems to global or I'm missing something.
> 
> This patch extends the existing Flexcan platform driver for ARM for the
> PowerPC using the device tree. Due to the nice integration of the device
> tree (of-platform) into the platform driver and devices, the difference
> are quite small (see patches 1..3). Apart from the endianess issue, only
> the clock needs to be handled in a common way. As ARM already uses the
> clk interface, we found it straight-forward to implement it for the
> P1010, or more general for the 85xx, as well, instead of using an
> additional helper function.

I see, that.  What concerns me is there are numerous clocks / frequencies that exist inside a MPC85xx/P1010 SOC.  The code I'm seeing does NOT seem to do anything to relate this clock JUST to the flexcan.

>> I still think the clk / freq info should be in the device tree and handled in the driver and NOT arch/powerpc platform code.
> 
> If I understand you correctly, you want the boot-loader to provide the
> relevant information by fixing up the device tree, which then can be
> handled arch-independently by the driver, right?

Yes, that is part of what I want.

- k--
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