[PATCH 1/2] usb: host: tegra: don't touch EMC clock

Lucas Stach dev at lynxeye.de
Wed Jan 23 04:45:26 EST 2013

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.
> Stephen,
> 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.


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