linux-kernel - Re: [PATCH 3/5] mtd: brcmnand: Optional DT flag to reset IPROC NAND controller

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Date:	Mon, 12 Oct 2015 14:27:42 -0700
From:	Brian Norris <computersforpeace@...il.com>
To:	Anup Patel <anup.patel@...adcom.com>
Cc:	Florian Fainelli <f.fainelli@...il.com>,
	Scott Branden <sbranden@...adcom.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	David Woodhouse <dwmw2@...radead.org>,
	Ray Jui <rjui@...adcom.com>,
	Pramod Kumar <pramodku@...adcom.com>,
	Vikram Prakash <vikramp@...adcom.com>,
	Sandeep Tripathy <tripathy@...adcom.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
	Rafal Milecki <zajec5@...il.com>
Subject: Re: [PATCH 3/5] mtd: brcmnand: Optional DT flag to reset IPROC NAND
 controller

Hi Anup,

On Wed, Oct 07, 2015 at 03:33:50AM +0000, Anup Patel wrote:
> > -----Original Message-----
> > From: Florian Fainelli [mailto:f.fainelli@...il.com]
> > 
> > On 06/10/15 15:25, Scott Branden wrote:
> > 
> > Then instead of adding a "reset flag" to Device Tree, another approach could be
> > to put the desired or currently configured exhaustive list of NAND timings in
> > Device Tree, and based on that you could have this:
> > 
> > - the NAND controller driver finds that these timings match the current
> > configuration, you are good to go
> > 
> > - the NAND controller drivers finds a difference in how current timings are
> > configured vs. desired timings, and issues a controller reset, prior to applying
> > new timing configuration
> 
> To add to this ...
> 
> The mechanism to reset is BRCM NAND controller is SOC specific so the
> SoC independent BRCM NAND driver (i.e. brcmnand.c) does not know how
> to reset the NAND controller.
> 
> For iProc SoC family, the NAND controller reset is through IDM register
> space which is only iomap'ed by iproc_nand.c.
> 
> We might end-up having one more SoC specific callback which will be
> Provided by iproc_nand.c to brcmnand.c.
> 
> > 
> > - no timings are configured, reset the controller and use existing auto-detection
> > capabilities like ONFI modes
> > 
> > Typically you would put the desired timings instead of the currently configured
> > timings though..
> 
> Overall, it would good to support timing parameters through DT or ONFI but
> for now have we can rely on reset and auto-devid configuration.

I don't want to support a DT property that is only used as a workaround
for the right solution. That means the property may quickly become
obsolete, yet we have to support it forever.


> > >>     compatible = "brcm,iproc-nand-ns2", ...;
> > >>
> > > As described above - the option is not SoC specific.  It is system
> > > specific.  In some systems we may wish to reset the NAND controller in
> > > linux.  In some we may wish to rely on initialization that has already
> > > been done to speed up boot times.
> > 
> > It seems to me like having this property is fine as long as you are describing that
> > the controller *needs* a reset to operate properly, it does not strike me as a
> > particularly well suited property if its side effect and main usage is to keep or
> > wipe-out existing NAND timings.
> 
> IMHO, having SoC specific compatible string for NS2 is like saying
> NAND controller on NS2 is different from other iProc SoCs whereas
> Having optional DT flags for quirks/work-arounds (e.g. NAND controller
> reset) is like saying NAND controller on NS2 same as other iProc SoCs
> but some additional programming is required. 

OK... so what is the reason that you have to reset the controller on NS2
and not Cygnus? Is it a SoC difference (i.e., compatible string)?
Firmware/bootloader difference? So far, all statements have been
non-specific, AFAICT.

Brian
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