From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Warren Subject: Re: [PATCH 1/2] usb: host: tegra: don't touch EMC clock Date: Wed, 23 Jan 2013 09:17:14 -0700 Message-ID: <51000D0A.4010007@wwwdotorg.org> References: <1358900903-27654-1-git-send-email-swarren@wwwdotorg.org> <1358934326.1540.32.camel@tellur> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1358934326.1540.32.camel@tellur> Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Lucas Stach Cc: Venu Byravarasu , Alan Stern , Greg Kroah-Hartman , "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" , "linux-usb-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Stephen Warren , Venkat Moganty List-Id: linux-tegra@vger.kernel.org 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-u79uwXL29TY76Z2rM5mHXA@public.gmane.org [mailto:linux-tegra- >>> owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.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-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; linux-arm- >>> kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org; linux-usb-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; Stephen Warren >>> Subject: [PATCH 1/2] usb: host: tegra: don't touch EMC clock >>> >>> From: Stephen Warren >>> >>> 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. I agree. 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.