linux-kernel - Re: [RFC PATCH 0/8] Add TI EMIF SDRAM controller driver

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Date:	Thu, 16 Feb 2012 08:23:59 -0800
From:	Greg KH <greg@...ah.com>
To:	Santosh Shilimkar <santosh.shilimkar@...com>
Cc:	akpm@...ux-foundation.org, Aneesh V <aneesh@...com>,
	linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/8] Add TI EMIF SDRAM controller driver

On Thu, Feb 16, 2012 at 04:21:11PM +0530, Santosh Shilimkar wrote:
> Andrew, Greg,
> 
> On Saturday 04 February 2012 05:46 PM, Aneesh V wrote:
> > Add a driver for the EMIF SDRAM controller used in TI SoCs
> > 
> > EMIF is an SDRAM controller that supports, based on its revision,
> > one or more of LPDDR2/DDR2/DDR3 protocols.This driver adds support
> > for LPDDR2.
> > 
> > The driver supports the following features:
> > - Calculates the DDR AC timing parameters to be set in EMIF
> >   registers using data from the device data-sheets and based
> >   on the DDR frequency. If data from data-sheets is not available
> >   default timing values from the JEDEC spec are used. These
> >   will be safe, but not necessarily optimal
> > - API for changing timings during DVFS or at boot-up
> > - Temperature alert configuration and handling of temperature
> >   alerts, if any for LPDDR2 devices
> >   * temperature alert is based on periodic polling of MR4 mode
> >     register in DDR devices automatically performed by hardware
> >   * timings are de-rated and brought back to nominal when
> >     temperature raises and falls respectively
> > - Cache of calculated register values to avoid re-calculating
> >   them
> > 
> > The driver will need some minor updates when it is eventually
> > integrated with DVFS. This can not be done now as DVFS support
> > is not available yet in mainline.
> > 
> > Discussions with Santosh Shilimkar <santosh.shilimkar@...com>
> > were immensely helpful in shaping up the interfaces. Vibhore Vardhan
> > <vvardhan@...il.com> did the initial code snippet for thermal
> > handling.
> > 
> > Testing: 
> > - The driver is tested on OMAP4430 SDP.
> > - The driver in a slightly adapted form is also tested on OMAP5.
> > - Since mainline kernel doesn't have DVFS support yet,
> >   testing was done using a test module.
> > - Temperature alert handling was tested with simulated interrupts
> >   and faked temperature values as testing all cases in real-life
> >   scenarios is difficult.
> > 
> [...]
> 
> >  arch/arm/mach-omap2/omap_hwmod_44xx_data.c |  110 ++
> >  drivers/misc/Kconfig                       |   20 +
> >  drivers/misc/Makefile                      |    2 +
> >  drivers/misc/emif.c                        | 1522 ++++++++++++++++++++++++++++
> >  drivers/misc/emif_regs.h                   |  461 +++++++++
> >  drivers/misc/jedec_ddr_data.c              |  141 +++
> >  include/linux/emif.h                       |  257 +++++
> >  include/linux/jedec_ddr.h                  |  174 ++++
> 
> Any suggestion on where this driver can reside. It's a memory
> controller driver which supports standard DDR functionality
> as per JDEC specs including thermal alert. On top of
> that it does support DVFS using the TI PRCM IP block.

I don't know what any of those TLA words mean, so I really can't suggest
where this code should go.  But just from this diffstat, it looks like
you are creating a new user/kernel interface, without documenting it
anywhere, which isn't ok.

greg k-h
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