lkml.org 
[lkml]   [2010]   [Jul]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectMeaning of clk_round_rate()?
  What is the meaning of clk_round_rate() in the clk API 
(include/linux/clk.h)? The function documentation says "adjust a rate to
the exact rate a clock can provide". That seems pretty vague. I'm lead
to believe that it rounds the rate to the closest rate supported. Is
that correct? Is there some sort of error margin where beyond that it's
no longer possible to be rounded? 0.5%? 1%?

Assuming it's doing closest matching, I don't see how it's very useful
in practice. Some users of clk_round_rate() are blindly searching up and
down in the frequency space until they find a suitable rate (see
sound/atmel/abdac.c and sound/spi/at73c213.c). These drivers might be
better served by something like a clk_round_rate_up() and a
clk_round_rate_down() which would round the rate to the nearest higher
and lower frequency respectively without requiring complex loops around
clk_round_rate().

In addition, an up/down rounding approach would make it simpler for
drivers to find a min/max rate (for example display panels have a max
frequency they can support).

A similar approach was suggested by David Brownell [1] but nothing came
of it.

[1] http://article.gmane.org/gmane.linux.ports.arm.kernel/38076

--
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.



\
 
 \ /
  Last update: 2010-07-14 20:09    [W:0.057 / U:8.676 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site