From: mperttunen@nvidia.com (Mikko Perttunen)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 5/8] of: Add Tegra124 EMC bindings
Date: Mon, 14 Jul 2014 15:28:54 +0300 [thread overview]
Message-ID: <53C3CD06.8070907@nvidia.com> (raw)
In-Reply-To: <20140714111007.GB31460@ulmo>
On 14/07/14 14:10, Thierry Reding wrote:
> * PGP Signed by an unknown key
>
> On Mon, Jul 14, 2014 at 01:54:36PM +0300, Mikko Perttunen wrote:
>> On 14/07/14 13:29, Thierry Reding wrote:
>>>> Old Signed by an unknown key
>>> ...
>>>> Yes, this sounds sensible. I'll make such a patch. I suppose having another
>>>> timings table in the MC node with just the rate and mc-burst-data would
>>>> separate the concerns best. It occurs to me that we could also write the
>>>> regs in the pre-rate change notifier, but this would turn the dependency
>>>> around and would mean that the regs are not written when entering backup
>>>> rates. The latter shouldn't be a problem but the reversed dependency would,
>>>> so I guess a custom function is the way to go, and we need to add at least
>>>> one anyway.
>>>
>>> It sounds like maybe moving enough code and data into the MC driver to
>>> handle frequency changes would be a good move. From the above it sounds
>>> like all the MC driver needs to know is that a frequency change is about
>>> to happen and what the new frequency is.
>>>
>>> In addition to exposing things like number of DRAM banks, etc.
>>>
>>
>> Yes, so there are two ways to do this:
>> 1) EMC calls tegra_mc_emem_update(freq) at the correct time
>> 2) MC has an optional clock phandle to the EMC clock and registers a
>> pre-change notifier.
>>
>> Both work, but the dependency is reversed. In both cases, the other driver
>> is also optional. In the first case, the EMC driver can give a warning if
>> the call fails. (As mentioned, if the MC_EMEM updates don't happen, things
>> still work but potentially with a hefty perf loss.)
>> TBH, I haven't yet decided which one is better. If you have an opinion,
>> I'll go with it.
>
> I think I prefer 1. Using an explicit call into the MC driver allow us
> to precisely determine the moment in time when the registers should be
> updated. The pre-change notifier, as I understand it, doesn't give us
> that. Also, the notifier doesn't give us a way to determine success or
> failure of the MC call.
Indeed. I'll go with this.
>
>>>> The downstream kernel also overwrites most LA registers during EMC rate
>>>> change without regard for the driver-set values, and we might have to read
>>>> those values from the device tree too. Upstream can do this in rate change
>>>> notifiers if needed. I'll look into this a bit more.
>>>
>>> As I understand it, the latency allowance should be specified in terms
>>> of the maximum amount of time that requests are delayed, so that the
>>> proper values for the LA registers can be recomputed on an EMC rate
>>> change.
>>
>> That's how I understand it too, but in downstream, the LA register values
>> are hardcoded into EMC tables in platform data/DTS that are just written
>> into the LA registers as-is during rate change.
>
> Hehe, well, we don't want any of that upstream. =) If it can be computed
> at runtime, then let's compute it. Also, if it's encoded in platform
> data or DTS, then there's no way it can be adjusted based on use-case.
> For example if you have a device with two display outputs (an internal
> panel and HDMI for example) but you never have HDMI plugged in, then
> there's no reason why you would want to program the latency allowance
> for the second display controller. If you provide the values in a static
> frequency/register value table, then you need to account for any
> possible scenario up front, irrespective of what (if any) HDMI monitor
> is attached.
Yeah, I guess the values in downstream must be designed for the worst
case :P the strange thing is that downstream also has an API for drivers
to specify their requirements. I guess the clients that have hardcoded
values and that use the API don't overlap. But I definitely agree that
on upstream we can have something nicer.
>
> Thierry
>
> * Unknown Key
> * 0x7F3EB3A1
>
next prev parent reply other threads:[~2014-07-14 12:28 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-11 14:18 [PATCH 0/8] Tegra124 EMC (external memory controller) support Mikko Perttunen
2014-07-11 14:18 ` [PATCH 1/8] clk: tegra124: Remove old emc_mux and emc clocks Mikko Perttunen
2014-07-11 14:18 ` [PATCH 2/8] ARM: tegra: Remove TEGRA124_CLK_EMC from tegra124-car.h Mikko Perttunen
2014-07-21 22:37 ` Stephen Warren
2014-07-29 8:28 ` Mikko Perttunen
2014-07-11 14:18 ` [PATCH 3/8] ARM: tegra: Add PLL_M_UD and PLL_C_UD to tegra124-car binding header Mikko Perttunen
2014-08-25 17:41 ` Stephen Warren
2014-09-17 13:41 ` Peter De Schrijver
2014-07-11 14:18 ` [PATCH 4/8] clk: tegra124: Add PLL_M_UD and PLL_C_UD clocks Mikko Perttunen
2014-07-11 14:18 ` [PATCH 5/8] of: Add Tegra124 EMC bindings Mikko Perttunen
2014-07-11 14:51 ` Thierry Reding
2014-07-11 16:01 ` Mikko Perttunen
2014-07-14 7:55 ` Mikko Perttunen
2014-07-14 8:15 ` Thierry Reding
2014-07-14 9:06 ` Mikko Perttunen
2014-07-14 9:31 ` Thierry Reding
2014-07-14 9:57 ` Mikko Perttunen
2014-07-14 10:29 ` Thierry Reding
2014-07-14 10:54 ` Mikko Perttunen
2014-07-14 11:10 ` Thierry Reding
2014-07-14 12:28 ` Mikko Perttunen [this message]
2014-07-11 16:43 ` Andrew Bresticker
2014-07-11 16:48 ` Mikko Perttunen
2014-07-21 21:28 ` Stephen Warren
2014-07-21 22:52 ` Andrew Bresticker
2014-07-22 16:45 ` Stephen Warren
2014-07-22 17:22 ` Andrew Bresticker
2014-07-22 17:34 ` Stephen Warren
2014-07-29 8:30 ` Mikko Perttunen
2014-07-29 15:49 ` Stephen Warren
2014-07-31 10:48 ` Mikko Perttunen
2014-07-31 11:05 ` Mikko Perttunen
2014-07-31 15:32 ` Stephen Warren
2014-07-21 22:36 ` Stephen Warren
2014-07-11 14:18 ` [PATCH 6/8] ARM: tegra: Add EMC to Tegra124 device tree Mikko Perttunen
2014-07-11 14:18 ` [PATCH 7/8] ARM: tegra: Add EMC timings to Jetson TK1 " Mikko Perttunen
2014-07-11 14:18 ` [PATCH 8/8] clk: tegra: Add EMC clock driver Mikko Perttunen
2014-07-22 16:57 ` Stephen Warren
2014-07-29 8:47 ` Mikko Perttunen
2014-07-29 20:19 ` Mike Turquette
2014-07-29 22:14 ` Stephen Warren
2014-07-30 9:34 ` Thierry Reding
2014-07-31 19:06 ` Mike Turquette
2014-07-31 19:53 ` Stephen Warren
2014-07-31 23:08 ` Mike Turquette
2014-08-01 6:31 ` Mikko Perttunen
2014-08-01 8:40 ` Thierry Reding
2014-08-25 17:40 ` [PATCH 0/8] Tegra124 EMC (external memory controller) support Stephen Warren
2014-08-26 7:42 ` Mikko Perttunen
2014-08-26 7:47 ` Thierry Reding
2014-08-26 8:02 ` Mikko Perttunen
2014-09-05 10:22 ` Tomeu Vizoso
2014-09-05 10:55 ` Mikko Perttunen
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