lkml.org 
[lkml]   [2014]   [Mar]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] spi: sc18is602: Don't be that restrictive with the maximum transfer speed
On Sun, Mar 16, 2014 at 06:47:50PM -0700, Guenter Roeck wrote:
> Commit 09e99bca8 (spi: sc18is602: Convert to let spi core validate
> transfer speed) made the maximum transfer speed much more restrictive
> than before. The transfer speed used to be adjusted to 1/4 of the chip
> clock rate if a higher transfer speed was requested. Now such transfers are
> simply rejected. With default settings, this causes, for example, a transfer
> request at 2 mbps to be rejected because the maximum speed with the default
> chip clock is 1.843 mbps.

> This is unnecessarily restrictive and causes unnecessary failures. Loosen
> the limit to accept transfers up to 50% of the clock rate and adjust
> the speed as needed when setting up the actualt transfer.

Given this description I'd expect to see a change in the core not a
driver - like the other fork of the thread said I'd expect to deal with
the issue by improving the constraint handling code.

> master->transfer_one_message = sc18is602_transfer_one;
> master->dev.of_node = np;
> master->min_speed_hz = hw->freq / 128;
> - master->max_speed_hz = hw->freq / 4;
> + master->max_speed_hz = hw->freq / 2;

That said, if this is something that the hardware can support it makes
sense to do it anyway - is there an actual spec constraint available?
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2014-03-17 13:41    [W:0.264 / U:0.384 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site