[PATCH 1/2] usb: host: tegra: don't touch EMC clock
swarren at wwwdotorg.org
Wed Jan 23 11:17:14 EST 2013
On 01/23/2013 02:45 AM, Lucas Stach wrote:
> Am Mittwoch, den 23.01.2013, 12:25 +0530 schrieb Venu Byravarasu:
>>> -----Original Message-----
>>> From: linux-tegra-owner at vger.kernel.org [mailto:linux-tegra-
>>> owner at vger.kernel.org] On Behalf Of Stephen Warren
>>> Sent: Wednesday, January 23, 2013 5:58 AM
>>> To: Alan Stern; Greg Kroah-Hartman; Stephen Warren
>>> Cc: Venu Byravarasu; linux-tegra at vger.kernel.org; linux-arm-
>>> kernel at lists.infradead.org; linux-usb at vger.kernel.org; Stephen Warren
>>> Subject: [PATCH 1/2] usb: host: tegra: don't touch EMC clock
>>> From: Stephen Warren <swarren at nvidia.com>
>>> Clock "emc" is for the External Memory Controller. The USB driver has no
>>> business touching this clock directly. Remove the code that does so.
>> This was primarily done to make sure that EMC is set to a minimum
>> frequency, below which data errors may occur during USB transfers.
>> If we plan to remove this, how should we make sure that the EMC
>> is programmed for the required frequency during USB transfers?
> You could use something like the API I added in "ARM: tegra: add EMC
> clock scaling API". This needs some rework and I looked into integrating
> this with the DEVFREQ framework, but I don't think it fits too well.
> Bandwidth requirements should always be communicated to the EMC driver
> and not described by clock rates.
Besides, on some boards there's an EMC scaling table defined already, so
the EMC driver is simply overriding the value the USB driver selects anyway.
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