linux-spi.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: "H Hartley Sweeten" <hartleys@visionengravers.com>
To: "Mike Frysinger" <vapier@gentoo.org>,
	<spi-devel-general@lists.sourceforge.net>,
	"David Brownell" <dbrownell@users.sourceforge.net>
Cc: "Yi Li" <yi.li@analog.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	<linux-kernel@vger.kernel.org>
Subject: RE: [spi-devel-general] [PATCH 2/2] mmc_spi: lock the SPI bus whenaccessing the card
Date: Thu, 17 Sep 2009 20:29:54 -0400	[thread overview]
Message-ID: <BD79186B4FD85F4B8E60E381CAEE190901D41E4C@mi8nycmail19.Mi8.com> (raw)
In-Reply-To: <1253224997-7422-2-git-send-email-vapier@gentoo.org>

On Thursday, September 17, 2009 3:03 PM, Mike Frysinger wrote:
> From: Yi Li <yi.li@analog.com>
> 
> The MMC/SPI spec does not play well with typical SPI design -- it often
> needs to send out a command in one message, read a response, then do some
> other arbitrary step.  Since we can't let another SPI client use the bus
> during this time, use the new SPI lock/unlock functions to provide the
> required exclusivity.
> 
> Signed-off-by: Yi Li <yi.li@analog.com>
> Signed-off-by: Mike Frysinger <vapier@gentoo.org>
> ---
>  drivers/mmc/host/mmc_spi.c |   29 ++---------------------------
>  1 files changed, 2 insertions(+), 27 deletions(-)
> 
> diff --git a/drivers/mmc/host/mmc_spi.c b/drivers/mmc/host/mmc_spi.c
> index a461017..a96e058 100644
> --- a/drivers/mmc/host/mmc_spi.c
> +++ b/drivers/mmc/host/mmc_spi.c
> @@ -1084,6 +1084,7 @@ static void mmc_spi_request(struct mmc_host *mmc, struct mmc_request *mrq)
>  #endif
>  
>  	/* issue command; then optionally data and stop */
> +	spi_lock_bus(host->spi);
>  	status = mmc_spi_command_send(host, mrq, mrq->cmd, mrq->data != NULL);
>  	if (status == 0 && mrq->data) {
>  		mmc_spi_data_do(host, mrq->cmd, mrq->data, mrq->data->blksz);
> @@ -1092,7 +1093,7 @@ static void mmc_spi_request(struct mmc_host *mmc, struct mmc_request *mrq)
>  		else
>  			mmc_cs_off(host);
>  	}
> -
> +	spi_unlock_bus(host->spi);
>  	mmc_request_done(host->mmc, mrq);
>  }
>  
> @@ -1337,32 +1338,6 @@ static int mmc_spi_probe(struct spi_device *spi)
>  		return status;
>  	}
>  
> -	/* We can use the bus safely iff nobody else will interfere with us.
> -	 * Most commands consist of one SPI message to issue a command, then
> -	 * several more to collect its response, then possibly more for data
> -	 * transfer.  Clocking access to other devices during that period will
> -	 * corrupt the command execution.
> -	 *
> -	 * Until we have software primitives which guarantee non-interference,
> -	 * we'll aim for a hardware-level guarantee.
> -	 *
> -	 * REVISIT we can't guarantee another device won't be added later...
> -	 */
> -	if (spi->master->num_chipselect > 1) {
> -		struct count_children cc;
> -
> -		cc.n = 0;
> -		cc.bus = spi->dev.bus;
> -		status = device_for_each_child(spi->dev.parent, &cc,
> -				maybe_count_child);
> -		if (status < 0) {
> -			dev_err(&spi->dev, "can't share SPI bus\n");
> -			return status;
> -		}
> -
> -		dev_warn(&spi->dev, "ASSUMING SPI bus stays unshared!\n");
> -	}
> -
>  	/* We need a supply of ones to transmit.  This is the only time
>  	 * the CPU touches these, so cache coherency isn't a concern.
>  	 *

Removing the above block of code causes:

drivers/mmc/host/mmc_spi.c:1299: warning: 'maybe_count_child' defined but not used

That function should also be removed along with the "struct count_children"
definition.

Regards,
Hartley

  reply	other threads:[~2009-09-18  0:29 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-09-17 22:03 [PATCH 1/2] spi: new SPI bus lock/unlock functions Mike Frysinger
2009-09-17 22:03 ` [PATCH 2/2] mmc_spi: lock the SPI bus when accessing the card Mike Frysinger
2009-09-18  0:29   ` H Hartley Sweeten [this message]
2009-09-18  0:52     ` [PATCH 2/2 v2] " Mike Frysinger
2009-09-18 21:30       ` Andrew Morton
2009-09-17 22:45 ` [spi-devel-general] [PATCH 1/2] spi: new SPI bus lock/unlockfunctions H Hartley Sweeten
2009-09-17 22:53   ` Mike Frysinger
2009-09-18 23:00     ` H Hartley Sweeten
2009-09-19 19:11       ` Mike Frysinger
2009-09-21  8:08       ` Li Yi
2009-09-18 21:29 ` [PATCH 1/2] spi: new SPI bus lock/unlock functions Andrew Morton
2009-09-21  6:33   ` Li Yi
2009-09-21 13:36     ` Mike Frysinger
2009-09-22 14:15 ` Mike Frysinger
2009-12-16 22:49 ` [spi-devel-general] [PATCH 1/2] spi: new SPI bus lock/unlockfunctions H Hartley Sweeten
2009-12-16 23:00   ` Mike Frysinger

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=BD79186B4FD85F4B8E60E381CAEE190901D41E4C@mi8nycmail19.Mi8.com \
    --to=hartleys@visionengravers.com \
    --cc=akpm@linux-foundation.org \
    --cc=dbrownell@users.sourceforge.net \
    --cc=linux-kernel@vger.kernel.org \
    --cc=spi-devel-general@lists.sourceforge.net \
    --cc=vapier@gentoo.org \
    --cc=yi.li@analog.com \
    --subject='RE: [spi-devel-general] [PATCH 2/2] mmc_spi: lock the SPI bus whenaccessing the card' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).