On Wed, 2007-10-31 at 00:11 -0700, David Brownell wrote:
> 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.
>
IMO, the spi_transfer.speed_hz <= spi_board_info.max_speed_hz and if
spi_trasnfer.speed_hz is 0, we should use spi_board_info.max_speed_hz.
>From the meaning of max_speed_hz, the spi_transfer.speed_hz should not
beyond max_speed_hz.
In your explanation, the max_speed_hz is just a default value. the
transfer speed_hz can beyond max_speed_hz. We found the bug in M25P16
should be related this missing checking of the transfer speed_hz.
>
> > 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.)
>
OK, We check it on Blackfin board.
-Bryan Wu
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