From: swarren@wwwdotorg•org (Stephen Warren)
To: linux-arm-kernel@lists•infradead.org
Subject: [RFC PATCH 1/4] memory: tegra124-emc: Add EMC driver
Date: Tue, 17 Jun 2014 10:15:50 -0600 [thread overview]
Message-ID: <53A069B6.6070902@wwwdotorg.org> (raw)
In-Reply-To: <53A03186.3040703@collabora.com>
On 06/17/2014 06:16 AM, Tomeu Vizoso wrote:
> On 06/16/2014 10:02 PM, Stephen Warren wrote:
>> On 06/16/2014 07:35 AM, Tomeu Vizoso wrote:
>> This binding looks quite anaemic vs.
>> Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-emc.txt; I
>> would expect that this binding needs all the EMC register data from the
>> tegra20-emc binding too. Can the two bindings be identical?
>
> There's even less stuff needed right now, as all what ultimately the EMC
> driver does is call clk_set_rate on the EMC clock. As the T124 EMC
> driver gains more features, they should get more similar.
IIRC, even changing the EMC clock rate requires modifying the memory
controller's programming (e.g. delays/taps/tuning etc.). That's exactly
what the more complex stuff in the nvidia,tegra20-emc.txt is all about.
I not convinced that a driver that just modifies the clock rate without
adjusting the EMC programming will work reliably.
>>> +#ifdef CONFIG_TEGRA124_EMC
>>> +int tegra124_emc_reserve_bandwidth(unsigned int consumer, unsigned
>>> long rate);
>>> +void tegra124_emc_set_floor(unsigned long freq);
>>> +void tegra124_emc_set_ceiling(unsigned long freq);
>>> +#else
>>> +int tegra124_emc_reserve_bandwidth(unsigned int consumer, unsigned
>>> long rate)
>>> +{ return -ENODEV; }
>>> +void tegra124_emc_set_floor(unsigned long freq)
>>> +{ return; }
>>> +void tegra124_emc_set_ceiling(unsigned long freq)
>>> +{ return; }
>>> +#endif
>>
>> I'll repeat what I said off-list so that we can have the whole
>> conversation on the list:
>>
>> That looks like a custom Tegra-specific API. I think it'd be much better
>> to integrate this into the common clock framework as a standard clock
>> constraints API. There are other use-cases for clock constraints besides
>> EMC scaling (e.g. some in audio on Tegra, and I'm sure many on other
>> SoCs too).
>
> Yes, I wrote a bit in the cover letter about our requirements and how
> they map to the CCF. Could you please comment on that?
My comments remain the same. I believe this is something that belongs in
the clock driver, or at the least, some API that takes a struct clock as
its parameter, so that drivers can use the existing DT clock lookup
mechanism.
next prev parent reply other threads:[~2014-06-17 16:15 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-16 13:35 [RFC PATCH 0/4] Tegra124: EMC scaling Tomeu Vizoso
2014-06-16 13:35 ` [RFC PATCH 1/4] memory: tegra124-emc: Add EMC driver Tomeu Vizoso
2014-06-16 14:03 ` Mikko Perttunen
2014-06-16 20:02 ` Stephen Warren
2014-06-17 12:16 ` Tomeu Vizoso
2014-06-17 16:15 ` Stephen Warren [this message]
2014-06-17 16:59 ` Mikko Perttunen
2014-06-18 17:23 ` Tomeu Vizoso
2014-06-18 17:46 ` Stephen Warren
2014-06-18 22:03 ` Thierry Reding
2014-06-18 22:09 ` Stephen Warren
2014-06-18 23:14 ` Thierry Reding
2014-06-18 23:24 ` Stephen Warren
2014-06-18 22:00 ` Thierry Reding
2014-06-18 22:19 ` Stéphane Marchesin
2014-06-18 22:33 ` Stephen Warren
2014-06-18 23:20 ` Thierry Reding
2014-06-17 22:35 ` Thierry Reding
2014-06-18 8:57 ` Peter De Schrijver
2014-06-16 13:35 ` [RFC PATCH 2/4] ARM: tegra: Add Tegra124 EMC support Tomeu Vizoso
2014-06-17 22:38 ` Thierry Reding
2014-06-16 13:35 ` [RFC PATCH 3/4] drm/tegra: Request memory bandwidth for the display controller Tomeu Vizoso
2014-06-16 20:06 ` Stephen Warren
2014-06-17 22:43 ` Thierry Reding
2014-06-16 13:35 ` [RFC PATCH 4/4] cpufreq: tegra: Register a minimum EMC frequency based on the CPU clock Tomeu Vizoso
2014-06-16 14:08 ` Mikko Perttunen
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