linux-kernel - Re: [PATCH RFC 06/12] mmc: mmci: Add write delay to variant structure.

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Message-ID: <20140421220819.GA4468@saruman.home>
Date:	Mon, 21 Apr 2014 17:08:19 -0500
From:	Felipe Balbi <balbi@...com>
To:	<srinivas.kandagatla@...aro.org>
CC:	<linux-mmc@...r.kernel.org>, Russell King <linux@....linux.org.uk>,
	Chris Ball <chris@...ntf.net>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	<linux-kernel@...r.kernel.org>, <agross@...cinc.com>,
	<linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH RFC 06/12] mmc: mmci: Add write delay to variant
 structure.

Hi,

On Mon, Apr 21, 2014 at 10:48:18PM +0100, srinivas.kandagatla@...aro.org wrote:
> From: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
> 
> This patch adds write delay parameter required after each write to controller
> registers on some of the SOCs like Qualcomm ones. The delay parameter will
> provide information on how many clock cycle delay required after each write.
> 
> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
> ---
>  drivers/mmc/host/mmci.c |    8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/mmc/host/mmci.c b/drivers/mmc/host/mmci.c
> index 4f8d0ba..86bf330 100644
> --- a/drivers/mmc/host/mmci.c
> +++ b/drivers/mmc/host/mmci.c
> @@ -55,6 +55,8 @@ static unsigned int fmax = 515633;
>   *	      is asserted (likewise for RX)
>   * @fifohalfsize: number of bytes that can be written when MCI_TXFIFOHALFEMPTY
>   *		  is asserted (likewise for RX)
> + * @reg_write_delay: delay in number of clock cycles required after each write
> + *		     to controller registers.
>   * @sdio: variant supports SDIO
>   * @st_clkdiv: true if using a ST-specific clock divider algorithm
>   * @blksz_datactrl16: true if Block size is at b16..b30 position in datactrl register
> @@ -72,6 +74,7 @@ struct variant_data {
>  	unsigned int		datalength_bits;
>  	unsigned int		fifosize;
>  	unsigned int		fifohalfsize;
> +	unsigned int		reg_write_delay;
>  	bool			sdio;
>  	bool			st_clkdiv;
>  	bool			blksz_datactrl16;
> @@ -178,7 +181,12 @@ static inline u32 mmci_readl(struct mmci_host *host, u32 off)
>  
>  static inline void mmci_writel(struct mmci_host *host, u32 data, u32 off)
>  {
> +	struct variant_data *var = host->variant;
> +
>  	writel(data, host->base + off);
> +
> +	if (var->reg_write_delay && host->mclk)
> +		udelay(1 + ((var->reg_write_delay * USEC_PER_SEC)/host->mclk));

looks like this should be quirk flag instead of a write delay... No
strong feelings though, but it looks like the following would be better,
perhaps:

	if (host_is_qualcom(host))
		udelay(1 + ((3 * USEC_PER_SEC)/host->mclk));

-- 
balbi

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