linux-kernel - Re: [PATCH 2/2] i2c: designware-pci: set ideal HCNT, LCNT and SDA hold time value

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Date:	Mon, 10 Mar 2014 16:21:10 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Chew Chiau Ee <chiau.ee.chew@...el.com>
Cc:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] i2c: designware-pci: set ideal HCNT, LCNT and SDA
 hold time value

On Fri, Mar 07, 2014 at 10:12:51PM +0800, Chew Chiau Ee wrote:
> From: Chew, Chiau Ee <chiau.ee.chew@...el.com>
> 
> On Intel BayTrail, there was case whereby the resulting fast mode
> bus speed becomes slower (~20% slower compared to expected speed)
> if using the HCNT/LCNT calculated in the core layer. Thus, this
> patch is added to allow pci glue layer to pass in optimal
> HCNT/LCNT/SDA hold time values to core layer since the core
> layer supports cofigurable HCNT/LCNT/SDA hold time values now.
> 
> Signed-off-by: Chew, Chiau Ee <chiau.ee.chew@...el.com>
> ---
>  drivers/i2c/busses/i2c-designware-pcidrv.c |   34 ++++++++++++++++++++++++++++
>  1 files changed, 34 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-designware-pcidrv.c b/drivers/i2c/busses/i2c-designware-pcidrv.c
> index 87f2fc4..96417ca 100644
> --- a/drivers/i2c/busses/i2c-designware-pcidrv.c
> +++ b/drivers/i2c/busses/i2c-designware-pcidrv.c
> @@ -58,6 +58,14 @@ enum dw_pci_ctl_id_t {
>  	baytrail,
>  };
>  
> +struct scl_sda_cfg {
> +	u32 ss_hcnt;
> +	u32 fs_hcnt;
> +	u32 ss_lcnt;
> +	u32 fs_lcnt;
> +	u32 sda_hold;
> +};

'dw_' prefix for this struct name, please.

>  #define INTEL_MID_STD_CFG  (DW_IC_CON_MASTER |			\
> @@ -77,6 +86,21 @@ struct dw_pci_controller {
>  					I2C_FUNC_SMBUS_WORD_DATA |	\
>  					I2C_FUNC_SMBUS_I2C_BLOCK)
>  
> +/* BayTrail HCNT/LCNT/SDA_HOLD */
> +#define BYT_STD_MODE_HCNT	0x200
> +#define BYT_STD_MODE_LCNT	BYT_STD_MODE_HCNT
> +#define BYT_FAST_MODE_HCNT	0x55
> +#define BYT_FAST_MODE_LCNT	0x99
> +#define BYT_SDA_HOLD		0x6

I'd think you can use these values directly in the struct. They are not
supposed to be used outside anyhow.

> +static struct scl_sda_cfg byt_config = {
> +	.ss_hcnt	= BYT_STD_MODE_HCNT,
> +	.fs_hcnt	= BYT_FAST_MODE_HCNT,
> +	.ss_lcnt	= BYT_STD_MODE_LCNT,
> +	.fs_lcnt	= BYT_FAST_MODE_LCNT,
> +	.sda_hold	= BYT_SDA_HOLD,
> +};

I'd prefer no tabs before "=", just one space.

Thanks,

   Wolfram


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