RE: [PATCH 1/3] spi: Add addr_width field to struct spi_message

[Hou Zhiqiang <B48286@xxxxxxxxxxxxx>]

Hi Geert,

> -----Original Message-----
> From: geert.uytterhoeven@xxxxxxxxx [mailto:geert.uytterhoeven@xxxxxxxxx]
> On Behalf Of Geert Uytterhoeven
> Sent: 2015年5月11日 15:43
> To: Hou Zhiqiang-B48286
> Cc: linux-spi; Mark Brown; Hu Mingkai-B21284
> Subject: Re: [PATCH 1/3] spi: Add addr_width field to struct spi_message
> 
> On Sun, May 10, 2015 at 4:47 PM, Zhiqiang Hou <B48286@xxxxxxxxxxxxx>
> wrote:
> > From: Hou Zhiqiang <B48286@xxxxxxxxxxxxx>
> >
> > Make SPI controller can get address width of the SPI device.
> 
> What does "address wdith" mean? From your other patches, I infer it's
> either
> 24 or 32 bit addressing as used by nor-jedec ("m25p80").
> Why does the generic spi_message needs to have nor-jedec-specific fields?
> 

Yes, the address width is the address width of spi flash.
The reason to add this nor-jedec-specific field to spi_message is the eSPI controller
of Freescale limits the MAX transaction length(TRANLEN) to 0x10000 each transaction, so if the
data size transferred exceed the TRANLEN, the eSPI controller can only transfer data for
the first TRANLEN, and need to issue new write/read commands to complete the remainders.
So, eSPI controller need getting the address width of spi flash, and then calculate the
new address to initialize the new write/read commands.

> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-
> m68k.org
> 
> In personal conversations with technical people, I call myself a hacker.
> But when I'm talking to journalists I just say "programmer" or something
> like that.
>                                 -- Linus Torvalds

Thanks,
Zhiqiang
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