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

[Marek Vasut <marex@denx.de>]

On Friday, April 25, 2014 at 03:52:46 AM, Huang Shijie wrote:
> On Fri, Apr 25, 2014 at 04:42:33AM +0200, Marek Vasut wrote:
> > On Friday, April 25, 2014 at 03:34:36 AM, Huang Shijie wrote:
> > > On Tue, Apr 22, 2014 at 09:03:16AM -0500, Graham Moore wrote:
> > > > Some new Micron flash chips require reading the flag
> > > > status register to determine when operations have completed.
> > > > 
> > > > Furthermore, chips with multi-die stacks of the 65nm 256Mb QSPI also
> > > > require reading the status register before reading the flag status
> > > > register.
> > > > 
> > > > This patch adds support for the flag status register in the
> > > > n25q512ax3 and n25q00 Micron QSPI flash chips.
> > > > 
> > > > Signed-off-by: Graham Moore <grmoore@altera.com>
> > > > ---
> > > > V3:
> > > > Rebase to l2-mtd spinor branch.
> > > > V2:
> > > > Remove leading underscore in function names.
> > > > Remove type cast in dev_err call and use the proper format
> > > > specifier instead.
> > > > ---
> > > > 
> > > >  drivers/mtd/spi-nor/spi-nor.c |   51
> > > >  +++++++++++++++++++++++++++++++++++++++++
> > > >  include/linux/mtd/spi-nor.h
> > > >  
> > > >  |    4 ++++
> > > >  
> > > >  2 files changed, 55 insertions(+)
> > > > 
> > > > diff --git a/drivers/mtd/spi-nor/spi-nor.c
> > > > b/drivers/mtd/spi-nor/spi-nor.c index d6f44d5..24b84d8 100644
> > > > --- a/drivers/mtd/spi-nor/spi-nor.c
> > > > +++ b/drivers/mtd/spi-nor/spi-nor.c
> > > > @@ -48,6 +48,25 @@ static int read_sr(struct spi_nor *nor)
> > > > 
> > > >  }
> > > >  
> > > >  /*
> > > > 
> > > > + * Read the flag status register, returning its value in the
> > > > location + * Return the status register value.
> > > > + * Returns negative if error occurred.
> > > > + */
> > > > +static int read_fsr(struct spi_nor *nor)
> > > > +{
> > > > +	int ret;
> > > > +	u8 val;
> > > > +
> > > > +	ret = nor->read_reg(nor, SPINOR_OP_RDFSR, &val, 1);
> > > > +	if (ret < 0) {
> > > > +		pr_err("error %d reading FSR\n", ret);
> > > > +		return ret;
> > > > +	}
> > > > +
> > > > +	return val;
> > > > +}
> > > > +
> > > > +/*
> > > > 
> > > >   * Read configuration register, returning its value in the
> > > >   * location. Return the configuration register value.
> > > >   * Returns negative if error occured.
> > > > 
> > > > @@ -165,6 +184,32 @@ static int spi_nor_wait_till_ready(struct
> > > > spi_nor *nor)
> > > > 
> > > >  	return -ETIMEDOUT;
> > > >  
> > > >  }
> > > > 
> > > > +static int spi_nor_wait_till_fsr_ready(struct spi_nor *nor)
> > > > +{
> > > > +	unsigned long deadline;
> > > > +	int sr;
> > > > +	int fsr;
> > > > +
> > > > +	deadline = jiffies + MAX_READY_WAIT_JIFFIES;
> > > > +
> > > > +	do {
> > > > +		cond_resched();
> > > > +
> > > > +		sr = read_sr(nor);
> > > > +		if (sr < 0)
> > > > +			break;
> > > > +		else if (!(sr & SR_WIP)) {
> > > > +			fsr = read_fsr(nor);
> > > > +			if (fsr < 0)
> > > > +				break;
> > > > +			if (fsr & FSR_READY)
> > > > +				return 0;
> > > > +		}
> > > > +	} while (!time_after_eq(jiffies, deadline));
> > > > +
> > > > +	return -ETIMEDOUT;
> > > > +}
> > > > +
> > > > 
> > > >  /*
> > > >  
> > > >   * Service routine to read status register until ready, or timeout
> > > >   occurs. * Returns non-zero if error.
> > > > 
> > > > @@ -402,6 +447,7 @@ struct flash_info {
> > > > 
> > > >  #define	SECT_4K_PMC		0x10	/* SPINOR_OP_BE_4K_PMC 
works
> > 
> > uniformly */
> > 
> > > >  #define	SPI_NOR_DUAL_READ	0x20    /* Flash supports Dual 
Read */
> > > >  #define	SPI_NOR_QUAD_READ	0x40    /* Flash supports Quad 
Read */
> > > > 
> > > > +#define	USE_FSR			0x80	/* use flag status 
register */
> > > > 
> > > >  };
> > > >  
> > > >  #define INFO(_jedec_id, _ext_id, _sector_size, _n_sectors, _flags)	\
> > > > 
> > > > @@ -488,6 +534,8 @@ const struct spi_device_id spi_nor_ids[] = {
> > > > 
> > > >  	{ "n25q128a13",  INFO(0x20ba18, 0, 64 * 1024,  256, 0) },
> > > >  	{ "n25q256a",    INFO(0x20ba19, 0, 64 * 1024,  512, SECT_4K) },
> > > >  	{ "n25q512a",    INFO(0x20bb20, 0, 64 * 1024, 1024, SECT_4K) },
> > > > 
> > > > +	{ "n25q512ax3",  INFO(0x20ba20, 0, 64 * 1024, 1024, USE_FSR) },
> > > > +	{ "n25q00",      INFO(0x20ba21, 0, 64 * 1024, 2048, USE_FSR) },
> > > > 
> > > >  	/* PMC */
> > > >  	{ "pm25lv512",   INFO(0,        0, 32 * 1024,    2, SECT_4K_PMC) 
},
> > > > 
> > > > @@ -965,6 +1013,9 @@ int spi_nor_scan(struct spi_nor *nor, const
> > > > struct spi_device_id *id,
> > > > 
> > > >  	else
> > > >  	
> > > >  		mtd->_write = spi_nor_write;
> > > > 
> > > > +	if (info->flags & USE_FSR)
> > > > +		nor->wait_till_ready = spi_nor_wait_till_fsr_ready;
> > > > +
> > > 
> > > 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 
doesn't seem right to me, but please correct me if I'm wrong ...