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Subject: Re: [PATCH] mmc: sdhci-omap: Workaround errata regarding SDR104/HS200
 tuning failures (i929)
To:     Ulf Hansson <ulf.hansson@linaro.org>
CC:     Kishon <kishon@ti.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>
References: <20181129190503.6040-1-faiz_abbas@ti.com>
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 <c4704766-7a58-8aa4-6bc0-b9373b15096c@ti.com>
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 <CAPDyKFrLzEfGKkC3K9znjJUKO1MUjdBpaL0HEtHYOzbAgNO-fg@mail.gmail.com>
From:   Faiz Abbas <faiz_abbas@ti.com>
Message-ID: <e19a5c39-028e-8dda-aa0a-3968a213cd47@ti.com>
Date:   Mon, 10 Dec 2018 19:37:31 +0530
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Hi,

On 10/12/18 7:15 PM, Ulf Hansson wrote:
> On Mon, 10 Dec 2018 at 14:23, Faiz Abbas <faiz_abbas@ti.com> wrote:
>>
>> Hi Uffe,
>>
>> On 05/12/18 7:20 PM, Ulf Hansson wrote:
>>> On Fri, 30 Nov 2018 at 06:53, Faiz Abbas <faiz_abbas@ti.com> wrote:
>>>>
>>>> Hi Kishon,
>>>>
>>>> On 30/11/18 10:10 AM, Kishon Vijay Abraham I wrote:
>>>>> Hi Faiz,
>>>>>
>>>>> On 30/11/18 12:35 AM, Faiz Abbas wrote:
>>>>>> Errata i929 in certain OMAP5/DRA7XX/AM57XX silicon revisions
>>>>>> (SPRZ426D - November 2014 - Revised February 2018 [1]) mentions
>>>>>> unexpected tuning pattern errors. A small failure band may be present
>>>>>> in the tuning range which may be missed by the current algorithm.
>>>>>> Furthermore, the failure bands vary with temperature leading to
>>>>>> different optimum tuning values for different temperatures.
>>>>>>
>>>>>> As suggested in the related Application Report (SPRACA9B - October 2017
>>>>>> - Revised July 2018 [2]), tuning should be done in two stages.
>>>>>> In stage 1, assign the optimum ratio in the maximum pass window for the
>>>>>> current temperature. In stage 2, if the chosen value is close to the
>>>>>> small failure band, move away from it in the appropriate direction.
>>>>>>
>>>>>> References:
>>>>>> [1] http://www.ti.com/lit/pdf/sprz426
>>>>>> [2] http://www.ti.com/lit/pdf/SPRACA9
>>>>>>
>>>>>> Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
>>>>>> ---
...
>>>>>
>>>>> Can't we get thermal zone once during probe?
>>>>>
>>>>
>>>> Tuning is also (ideally) supposed to happen only once per enumeration.
>>>> Also it doesn't make sense to get a thermal zone for lower speed systems
>>>> that won't do tuning.
>>>
>>> Currently sdhci-omap calls pm_runtime_get_sync() during probe, and
>>> then keeps the host device runtime resumed until ->remove() is called
>>> on it. I assume you are going to change that, at some point!?
>>>
>>> In other words, what will happen to the host device when it becomes
>>> runtime suspended? Is re-tuning needed when it gets runtime resumed,
>>> which is the case for many other sdhci variants?
>>
>> There are no plans to support runtime_suspend()/resume() any time in the
>> near future. If its ok with you, I would like to get this patch in
>> without any changes. We can change it in case a need for
>> runtime_suspend()/_resume() does arise.
> 
> Right, I am okay with that. Due to recent changes to sdhci-omap
> $subject patch doesn't apply, can you please rebase!?
> 
> Additionally, I realized that we should fold in patch updating the DT
> doc for sdhci-omap, adding the property for the thermal zone. I
> regards to that, I am wondering if "cpu_thermal", is really the
> correct name of the zone. The point is, I am guessing the zone could
> change along with the SoCs/platforms.
> 

As you have probably noticed, we are introducing a new driver
(sdhci_am654) for newer platforms. I don't foresee using sdhci-omap
driver with any other platforms. In case we do use it, we can add the dt
property at that point of time and default to "cpu_thermal" to maintain
dt compatibility.

Will rebase and send v2 if you are ok with above.

Thanks,
Faiz