linux-kernel - Re: [PATCH 1/2] drivers: mmc: add quirk SDHCI_QUIRK_CLOCK_DIV_ZERO

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Date:	Tue, 09 Jun 2015 17:44:10 +0900
From:	Jaehoon Chung <jh80.chung@...sung.com>
To:	Suneel Garapati <suneel.garapati@...inx.com>,
	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:	Ulf Hansson <ulf.hansson@...aro.org>, michals@...inx.com,
	sorenb@...inx.com, Adrian Hunter <adrian.hunter@...el.com>,
	Aisheng Dong <b29396@...escale.com>,
	Haibo Chen <haibo.chen@...escale.com>,
	Tim Kryger <tim.kryger@...il.com>,
	Shawn Guo <shawn.guo@...aro.org>, Yi Sun <yi.y.sun@...el.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>, stripathi@....com
Subject: Re: [PATCH 1/2] drivers: mmc: add quirk
 SDHCI_QUIRK_CLOCK_DIV_ZERO_BROKEN

Hi,

On 06/09/2015 04:31 PM, Suneel Garapati wrote:
> adds quirk for controllers whose clock divider zero is broken,
> sdhci_set_clock function will incorporate this modification.
> 
> Signed-off-by: Suneel Garapati <suneel.garapati@...inx.com>
> ---
>  drivers/mmc/host/sdhci.c | 4 ++++
>  drivers/mmc/host/sdhci.h | 2 ++
>  2 files changed, 6 insertions(+)
> 
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index 1b4861d..087327e 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -1210,6 +1210,10 @@ void sdhci_set_clock(struct sdhci_host *host, unsigned int clock)
> 			}
> 			real_div = div;
> 			div >>= 1;
> +			if ((host->quirks2 & SDHCI_QUIRK2_CLOCK_DIV_ZERO_BROKEN)
> +				&& !div && host->max_clk <= 25000000) {
> +				div = 1;
> +			}

I can't understand fully. how can it be broken for divider zero?
When formatting error is occurred, do you check really clock value?
I think your patch looks like just hard-coding for control clock.

Best Regards,
Jaehoon Chung

> 		}
> 	} else {
> 		/* Version 2.00 divisors must be a power of 2. */
> diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h
> index 5521d29..67046ca 100644
> --- a/drivers/mmc/host/sdhci.h
> +++ b/drivers/mmc/host/sdhci.h
> @@ -409,6 +409,8 @@ struct sdhci_host {
>  #define SDHCI_QUIRK2_SUPPORT_SINGLE			(1<<13)
>  /* Controller broken with using ACMD23 */
>  #define SDHCI_QUIRK2_ACMD23_BROKEN			(1<<14)
> +/* Broken Clock divider zero in controller */
> +#define SDHCI_QUIRK2_CLOCK_DIV_ZERO_BROKEN		(1<<15)
> 
> 	int irq;		/* Device IRQ */
> 	void __iomem *ioaddr;	/* Mapped address */
> --
> 2.1.2
> --
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