linux-kernel - Re: [PATCH 3/6] atmel-mci: Optional controller reset before every command

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Date:	Wed, 17 Jun 2009 10:32:22 +0200
From:	Marc Pignat <marc.pignat@...s.ch>
To:	linux-arm-kernel@...ts.arm.linux.org.uk
Cc:	Rob Emanuele <rob@...nuele.us>, nicolas.ferre@...el.com,
	haavard.skinnemoen@...el.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] atmel-mci: Optional controller reset before every command

Hi!

On Wednesday 17 June 2009 02:54:36 Rob Emanuele wrote:
> This patch adds the compile time configuration option for the atmel-mci driver to reset the Atmel MCI controller before every command.
> 
> This is sometimes needed for the Atmel controller / board to function properly.
> 
> Signed-off-by: Rob Emanuele <rob@...nuele.us>
> ---
>  drivers/mmc/host/Kconfig     |   10 ++++++++++
>  drivers/mmc/host/atmel-mci.c |   11 ++++++++++-
>  2 files changed, 20 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/mmc/host/Kconfig b/drivers/mmc/host/Kconfig
> index a0eaf69..5875125 100644
> --- a/drivers/mmc/host/Kconfig
> +++ b/drivers/mmc/host/Kconfig
> @@ -161,6 +161,16 @@ config MMC_ATMELMCI
>  
>  endchoice
>  
> +config MMC_ATMELMCI_ALWAYS_RESET
> +	bool "Reset before every request.  Sometimes needed for buggy chips."
> +	depends on MMC_ATMELMCI
> +	help
> +	  There are reports that some buggy controllers work better
> +	  with a reset before every command.  This may improve your
> +	  controller's reliability.
> +
> +	  If unsure, say N.
> +
>  config MMC_ATMELMCI_DMA
>  	bool "Atmel MCI DMA support (EXPERIMENTAL)"
>  	depends on MMC_ATMELMCI && AVR32 && DMA_ENGINE && EXPERIMENTAL
> diff --git a/drivers/mmc/host/atmel-mci.c b/drivers/mmc/host/atmel-mci.c
> index 98b25de..e5894f6 100644
> --- a/drivers/mmc/host/atmel-mci.c
> +++ b/drivers/mmc/host/atmel-mci.c
> @@ -63,6 +63,15 @@ struct atmel_mci_dma {
>  #endif
>  };
>  
> +/*
> + * Configuration options from the kernel config
> + */
> +#ifdef CONFIG_MMC_ATMELMCI_ALWAYS_RESET
> +#define MMC_ALWAYS_RESET 1
> +#else
> +#define MMC_ALWAYS_RESET 0
> +#endif

Some chips are known to hang after (some) transfer. There is no need for this
configuration option, I think we should just do : 

#define MMC_ALWAYS_RESET (cpu_is_at91rm9200() || add_your_cpu_name_here())

> +
>  /**
>   * struct atmel_mci - MMC controller state shared between all slots
>   * @lock: Spinlock protecting the queue and associated data.
> @@ -720,7 +729,7 @@ static void atmci_start_request(struct atmel_mci *host,
>  	host->completed_events = 0;
>  	host->data_status = 0;
>  
> -	if (host->need_reset) {
> +	if (host->need_reset || MMC_ALWAYS_RESET) {
>  		mci_writel(host, CR, MCI_CR_SWRST);
>  		mci_writel(host, CR, MCI_CR_MCIEN);
>  		mci_writel(host, MR, host->mode_reg);

Another option is to always reset the controller.

The reset operation won't hurt, it is simple and fast, and the code will be
simpler and better tested.

Best regards

Marc
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