lkml.org 
[lkml]   [2006]   [Apr]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [spi-devel-general] Re: [PATCH] spi: Added spi master driver for Freescale MPC83xx SPI controller
Date

On Apr 7, 2006, at 11:09 AM, David Brownell wrote:

> On Friday 07 April 2006 2:16 am, Vitaly Wool wrote:
>> Hi,
>>
>>> I guess I'm surprised you're not using txrx_buffers() and having
>>> that whole thing be IRQ driven, so the per-word cost eliminates
>>> the task scheduling. You already paid for IRQ handling ... why
>>> not have it store the rx byte into the buffer, and write the tx
>>> byte froom the other buffer? That'd be cheaper than what you're
>>> doing now ... in both time and code. Only wake up a task at
>>> the end of a given spi_transfer().
>>>
>> I might be completely wrong here, but I was asking myself this very
>> question, and it looks like that's the way to implement full duplex
>> transfers.
>
> Well, not the _only_ way. The polling-type txrx_word() calls are
> also full duplex. My point is more that it's bad/inefficient to
> incur both IRQ _and_ task switch overheads per word, when it would
> be a lot simpler to just have the IRQ handler do its normal job.
>
> (And that's even true if you've turned hard IRQ handlers into threads
> for PREEMPT_RT or whatever. In that case the "IRQ overhead" is a
> task switch, but you're still saving _additional_ task switches.)

This makes more sense about what I'm doing that is wasteful.
However, I'm not sure exactly where I should plug into things.

I think you are saying to continue using spi_bitbang_transfer &
spi_bitbang_work, but have spi_bitbang_work call my own bitbang-
>txrx_bufs().

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

\
 
 \ /
  Last update: 2006-04-07 19:07    [W:0.115 / U:0.332 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site