From: Grant Likely <grant.likely-s3s/WqlpOiPyB63q8FvJNQ@public.gmane.org>
To: Guennadi Liakhovetski
<g.liakhovetski-Mmb7MZpHnFY@public.gmane.org>,
spi-devel-general-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
Cc: Magnus Damm <magnus.damm-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Subject: Re: [PATCH 2/2] spi: bitbang: support the new SPI_BOARD_FLAG_RELEASE_CS flag
Date: Sat, 17 Mar 2012 22:42:13 +0000 [thread overview]
Message-ID: <20120317224213.ED0FF3E03CC@localhost> (raw)
In-Reply-To: <Pine.LNX.4.64.1203152230190.2988-0199iw4Nj15frtckUFj5Ag@public.gmane.org>
On Thu, 15 Mar 2012 22:32:14 +0100 (CET), Guennadi Liakhovetski <g.liakhovetski-Mmb7MZpHnFY@public.gmane.org> wrote:
> By supporting the new SPI_BOARD_FLAG_RELEASE_CS flag we let underlying
> hardware drivers implement more efficient runtime power-management.
>
> Signed-off-by: Guennadi Liakhovetski <g.liakhovetski-Mmb7MZpHnFY@public.gmane.org>
> ---
> drivers/spi/spi-bitbang.c | 22 ++++++++++------------
> 1 files changed, 10 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/spi/spi-bitbang.c b/drivers/spi/spi-bitbang.c
> index fe06e1b..c895d85 100644
> --- a/drivers/spi/spi-bitbang.c
> +++ b/drivers/spi/spi-bitbang.c
> @@ -347,17 +347,14 @@ static void bitbang_work(struct work_struct *work)
> if (t->delay_usecs)
> udelay(t->delay_usecs);
>
> - if (!cs_change)
> - continue;
> - if (t->transfer_list.next == &m->transfers)
> - break;
> -
> - /* sometimes a short mid-message deselect of the chip
> - * may be needed to terminate a mode or command
> - */
> - ndelay(nsecs);
> - bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
> - ndelay(nsecs);
> + if (cs_change && !list_is_last(&t->transfer_list, &m->transfers)) {
> + /* sometimes a short mid-message deselect of the chip
> + * may be needed to terminate a mode or command
> + */
> + ndelay(nsecs);
> + bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
> + ndelay(nsecs);
> + }
> }
>
> m->status = status;
> @@ -367,7 +364,8 @@ static void bitbang_work(struct work_struct *work)
> * cs_change has hinted that the next message will probably
> * be for this chip too.
> */
> - if (!(status == 0 && cs_change)) {
> + if (!(status == 0 && cs_change) ||
> + spi->flags & SPI_BOARD_FLAG_RELEASE_CS) {
That's rather heavy handed, and will probably break drivers that lock the spi
bus to guarantee concurrent messages (like the MMC layer). I don't think you
can do it this way.
It might be okay to force CS disable if the spi bus hasn't been exclusively
locked. I know the comment talks about hinting (possibly for performance reasonse),
but I'm more interested in correctness at this point.
g.
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next prev parent reply other threads:[~2012-03-17 22:42 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-15 21:32 [PATCH 1/2] spi: add an SPI-device flag for systems, preferring power-efficiency Guennadi Liakhovetski
[not found] ` <Pine.LNX.4.64.1203152228430.2988-0199iw4Nj15frtckUFj5Ag@public.gmane.org>
2012-03-15 21:32 ` [PATCH 2/2] spi: bitbang: support the new SPI_BOARD_FLAG_RELEASE_CS flag Guennadi Liakhovetski
[not found] ` <Pine.LNX.4.64.1203152230190.2988-0199iw4Nj15frtckUFj5Ag@public.gmane.org>
2012-03-17 22:42 ` Grant Likely [this message]
2012-04-13 14:43 ` Guennadi Liakhovetski
[not found] ` <Pine.LNX.4.64.1204131625230.16773-0199iw4Nj15frtckUFj5Ag@public.gmane.org>
2012-04-27 17:02 ` Grant Likely
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