[PATCH] mmc: core: add comment why sdio_reset is done at init time

[PATCH] mmc: core: add comment why sdio_reset is done at init time

[Philip Rakity]

sdio_reset sends a CMD52 to reset the sdio card.  This is
highly recommended for sdio cards being reinitialized.  Since
we do not know if the card is being reinitialized we just send
the command.  SD/eMMC cards are supposed to ignore the CMD
before the CMD0.  Document why we are doing this.

Signed-off-by: Philip Rakity <prakity@marvell.com>
---
 drivers/mmc/core/core.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 34a7e8c..d9fb0d3 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -1494,6 +1494,12 @@ static int mmc_rescan_try_freq(struct mmc_host *host, unsigned freq)
 		mmc_hostname(host), __func__, host->f_init);
 #endif
 	mmc_power_up(host);
+
+	/*
+	 * sdio_reset sends CMD52 to reset card.  Since we do not know
+	 * if the card is being re-initialzed just send it.  CMD52
+	 * should be ignored by SD/eMMC cards
+	 */
 	sdio_reset(host);
 	mmc_go_idle(host);
 
-- 
1.7.0.4

Re: [PATCH] mmc: core: add comment why sdio_reset is done at init time

[Chris Ball]

Hi Philip,

On Sun, Feb 13, 2011 at 11:12:28PM -0800, Philip Rakity wrote:
> 
> sdio_reset sends a CMD52 to reset the sdio card.  This is
> highly recommended for sdio cards being reinitialized.  Since
> we do not know if the card is being reinitialized we just send
> the command.  SD/eMMC cards are supposed to ignore the CMD
> before the CMD0.  Document why we are doing this.
> 
> Signed-off-by: Philip Rakity <prakity@marvell.com>
> ---
>  drivers/mmc/core/core.c |    6 ++++++
>  1 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 34a7e8c..d9fb0d3 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -1494,6 +1494,12 @@ static int mmc_rescan_try_freq(struct mmc_host *host, unsigned freq)
>  		mmc_hostname(host), __func__, host->f_init);
>  #endif
>  	mmc_power_up(host);
> +
> +	/*
> +	 * sdio_reset sends CMD52 to reset card.  Since we do not know
> +	 * if the card is being re-initialzed just send it.  CMD52
> +	 * should be ignored by SD/eMMC cards
> +	 */
>  	sdio_reset(host);
>  	mmc_go_idle(host);
>  

Thanks, pushed to mmc-next for .39.

-- 
Chris Ball   <cjb@laptop.org>   <http://printf.net/>
One Laptop Per Child