linux-kernel - Re: [PATCH] mmc: tegra: Add and use tegra_sdhci_get_max

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Message-ID: <39421023-0354-2af5-0a29-2299321a4259@nvidia.com>
Date:   Mon, 16 Jul 2018 20:47:02 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Aapo Vienamo <avienamo@...dia.com>
CC:     Ulf Hansson <ulf.hansson@...aro.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Marcel Ziswiler <marcel.ziswiler@...adex.com>,
        <linux-mmc@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mmc: tegra: Add and use tegra_sdhci_get_max_clock()


On 13/07/18 16:39, Aapo Vienamo wrote:

...

>>> that it returns the current clock rate of the host instead of the
>>> maximum one, which can lead to unnecessarily small clock rates.
>>>
>>> This differs from the previous implementation of
>>> tegra_sdhci_get_max_clock() in that it doesn't divide the result by two.  
>>
>> Why?
> 
> As far as I can tell the original tegra_sdhci_get_max_clock() was
> implemented this way in order to force sdhci_calc_clk() to always set
> the SDHCI clock divider to two on sdhci_set_clock(). The requirement to
> configure the SDHCI divider to two is specific to DDR50/52 modes on
> Tegra.
> 
> The .get_max_clock() callback retuning half of the actual maximum will
> result in HS200 and HS400 modes not being able to run at full speed.
> Another mechanism to enforce the divider requirement has to be figured
> out in order to enable DDR50/52 modes on Tegra SoCs.

OK, thanks. Ah I see Stefan's patch for doubling the clock. OK so that's fine.

Cheers
Jon

-- 
nvpublic