Re: [PATCH] spi: fix m25p80 when the cs_change hint is honored

[Baruch Siach <baruch-NswTu9S1W3P6gbPvEgmw2w@public.gmane.org>]

Hi David,

On Tue, May 19, 2009 at 09:34:14PM -0700, David Brownell wrote:
> Normal behavior of a spi_message is to keep the chipselect active
> during the entire message, then deactivate it after the last transfer.
> Setting the cs_change flag *changes* that behavior ... allowing either
> (a) brief mid-message deselection, usually to make a message hold a
> composite transaction, or else (b) hinting that immediate deselection
> isn't neccessary, as a possible performance tweak for some drivers.
> 
> Note that while (a) is mandatory -- drivers that can't do it must
> reject the messages using it -- (b) is optional.  When the next
> message goes to a different device, obviously the chip selection
> lines will need to change.

Thanks for the clarification.

If I understood correctly then, cs_change has two opposite meanings:

1. If cs_change != 0 in spi_transfer that is not the last in the current 
   spi_message, then deactivate the chip select between this spi_transfer and 
   the next.

2. If cs_change != 0 in spi_transfer that is that last in the current 
   spi_message, then the SPI controller is allowed to NOT deactivate the chip 
   select after the current spi_message.

Is this correct? If so would a clarification of the relevant text at 
include/linux/spi/spi.h be accepted?

baruch

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