[PATCH] powerpc/config: Disable the 4KiB erase granularity of SPI flash

[Zhiqiang Hou]

Hi Scott,

Thanks for your comments.

> -----Original Message-----
> From: Scott Wood [mailto:oss at buserror.net]
> Sent: 2016年4月7日 6:01
> To: Zhiqiang Hou <zhiqiang.hou at nxp.com>; linuxppc-dev at lists.ozlabs.org;
> benh at kernel.crashing.org; paulus at samba.org; mpe at ellerman.id.au
> Cc: Mingkai Hu <mingkai.hu at nxp.com>
> Subject: Re: [PATCH] powerpc/config: Disable the 4KiB erase granularity of SPI
> flash
> 
> On Wed, 2016-04-06 at 18:14 +0800, Zhiqiang Hou wrote:
> > From: Hou Zhiqiang <Zhiqiang.Hou at nxp.com>
> >
> > Disable the subsector (4KiB) erase granularity to speed up the erase
> > operation.
> >
> > Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou at nxp.com>
> > ---
> >  arch/powerpc/configs/85xx-hw.config | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/powerpc/configs/85xx-hw.config
> > b/arch/powerpc/configs/85xx -hw.config index 528ff0e..a0f4e70 100644
> > --- a/arch/powerpc/configs/85xx-hw.config
> > +++ b/arch/powerpc/configs/85xx-hw.config
> > @@ -77,6 +77,7 @@ CONFIG_MTD_PHYSMAP_OF=y
> CONFIG_MTD_PHYSMAP=y
> > CONFIG_MTD_PLATRAM=y  CONFIG_MTD_SPI_NOR=y
> > +# CONFIG_MTD_SPI_NOR_USE_4K_SECTORS is not set
> >  CONFIG_NETDEVICES=y
> >  CONFIG_NVRAM=y
> >  CONFIG_PATA_ALI=y
> 
> Is there a reason specific to 85xx to have a different default than every other
> platform except lpc18xx?  The description of MTD_SPI_NOR_USE_4K_SECTORS
> acknowledges that erase speed is a tradeoff.  Why is that concern more
> compelling on 85xx than elsewhere?
> 

I don't want to specify 85xx, but configs of fsl. I'm still confusing  about so many
configs. Will add other platforms if necessary.

For this patch, it takes about 13 mins to erase 64MiB by subsector erase command
(4KiB per time), but takes 2 mins by sector erase command(64KiB per time). It is
conspicuous decrease. Why it uses the 4KiB granularity by default, what's the
benefit?

Thanks,
Zhiqiang