linux-kernel - Re: [PATCH V3] Add support for flag status register on Micron chips.

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Date:	Mon, 28 Apr 2014 15:06:08 +0800
From:	Huang Shijie <b32955@...escale.com>
To:	Marek Vasut <marex@...x.de>
CC:	Huang Shijie <shijie8@...il.com>,
	Graham Moore <grmoore@...era.com>, <ggrahammoore@...il.com>,
	Geert Uytterhoeven <geert+renesas@...ux-m68k.org>,
	Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Jingoo Han <jg1.han@...sung.com>,
	<linux-kernel@...r.kernel.org>,
	Yves Vandervennet <rocket.yvanderv@...il.com>,
	<linux-mtd@...ts.infradead.org>,
	Insop Song <insop.song@...nspeed.com>,
	Alan Tull <atull@...era.com>,
	Sourav Poddar <sourav.poddar@...com>,
	Brian Norris <computersforpeace@...il.com>,
	"David Woodhouse" <dwmw2@...radead.org>,
	Dinh Nguyen <dinguyen@...era.com>
Subject: Re: [PATCH V3] Add support for flag status register on Micron
 chips.

On Mon, Apr 28, 2014 at 07:06:17AM +0200, Marek Vasut wrote:
> On Saturday, April 26, 2014 at 05:10:13 AM, Huang Shijie wrote:
> > On Sat, Apr 26, 2014 at 12:12:24AM +0200, Marek Vasut wrote:
> > > > > > the drivers may fills this hook itself, so the code should like this:
> > > > > >    --------------------------------------------------
> > > > > > 	
> > > > > > 	if ((info->flags & USE_FSR) &&
> > > > > > 	
> > > > > > 	       	nor->wait_till_ready == spi_nor_wait_till_fsr_ready)
> > > > > > 		
> > > > > > 		nor->wait_till_ready = spi_nor_wait_till_fsr_ready;
> > > > > > 		
> > > > > >    --------------------------------------------------
> > > > > 
> > > > > I sense a misdesign of the SPI NOR subsystem here. The subsystem and
> > > > > the driver compete for a function pointer here ? I guess one should
> > > > > have precedence in some way then ... and also, they should be two
> > > > > different pointers, where the subsystem decides which to use.
> > > > 
> > > > the subsystem do not decides which one to use, the driver decides which
> > > > one to use.
> > > > 
> > > > If driver has its own @wait_till_ready , it means the driver knows the
> > > > feature, and has implemented it in its own @wait_till_ready.
> > > > 
> > > > If the driver does not fill any wait_till_ready, it means the driver
> > > > will use the default @wait_till_ready. We can treat the
> > > > spi_nor_wait_till_fsr_ready as a default hook too.
> > > 
> > > I see the driver overwriting a hook previously set by the subsystem. This
> > 
> > not sure ;)
> > 
> > The driver set the hooks before the subsystem set these hooks.
> > 
> > If the driver has already set the @wait_till_ready hook before it calls
> > the spi_nor_scan, the subsystem will not set the hook anymore.
> > 
> > Please see the spi_nor_check().
> 
> Two things competing over the same pointer looks misdesigned to me. I will need 
> to dig into this one more time ...
Please refer to the code for NAND chip, the nand_get_flash_type() :

-----------------------------------------------------------
	/* Do not replace user supplied command function! */
	if (mtd->writesize > 512 && chip->cmdfunc == nand_command)
		chip->cmdfunc = nand_command_lp;
-----------------------------------------------------------

It uses the same logic: 
	" Do not replace user supplied command function!"

thanks
Huang Shijie
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