Re: [PATCH 09/14] Blackfin SPI driver: Fix SPI driver to work with SPI flash ST25P16 on bf548

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Tuesday 30 October 2007, Bryan Wu wrote:
> Maybe there are some confusion of mixing up the spi_trasnfer.speed_hz
> with the spi_device.max_speed_hz.
> 
> spi_device.max_speed_hz comes from spi_board_info.max_speed_hz, it is
> for the default max speed value.

It's initialized from board_info, yes.  Drivers can override it
using spi_setup().

One would expect they only override _downwards_ but that's not
guaranteed anywhere.  A driver might have a way to establish that
this particular board can run faster, for example.


> spi_transfer.speed_hz comes from upper applications for each spi
> transfer setting.

Certainly; all spi_transfer records come from applications!
If that value is zero, that transfer segment uses the limit
from the spi_device ... otherwise, it can differ.  Again,
the limits can vary based on devise characteristics; maybe
it can't feed data as fast for some commands.

(ISTR the M25P16 in $SUBJECT has two read commands, one of
which is only usable at clock rates below 33 MHz or so, but
most other commands can work above that speed just fine.)

- Dave
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[Index of Archives]     [Kernel Newbies]     [Netfilter]     [Bugtraq]     [Photo]     [Stuff]     [Gimp]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Video 4 Linux]     [Linux for the blind]     [Linux Resources]
  Powered by Linux