Re: [PATCH] i2c: designware: Add support for 16bit register access

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Hi,

second try, now with CC list. Forgive me the mangled lines.

My points to this discussion:

On 13/03/12 16:54, Stefan Roese wrote:
> The STM SPEAr platform can only access the i2c controller register
> via 16bit read/write functions. This patch adds support to
> automatically detect this 16bit access mode.
>
> Signed-off-by: Stefan Roese<sr@xxxxxxx>
> ---
>   drivers/i2c/busses/i2c-designware-core.c |   22 ++++++++++++++++++++--
>   drivers/i2c/busses/i2c-designware-core.h |    1 +
>   2 files changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
> index df87992..d1facbc 100644
> --- a/drivers/i2c/busses/i2c-designware-core.c
> +++ b/drivers/i2c/busses/i2c-designware-core.c
> @@ -164,7 +164,14 @@ static char *abort_sources[] = {
>
>   u32 dw_readl(struct dw_i2c_dev *dev, int offset)
>   {
> -    u32 value = readl(dev->base + offset);
> +    u32 value;
> +
> +    if (dev->access_16bit) {
> +        value = readw(dev->base + offset) |
> +            (readw(dev->base + offset + 2)<<  16);
> +    } else {
> +        value = readl(dev->base + offset);
> +    }

Since both blocks just have one statement, please remove the braces.

>
>       if (dev->swab)
>           return swab32(value);
> @@ -177,7 +184,12 @@ void dw_writel(struct dw_i2c_dev *dev, u32 b, int offset)
>       if (dev->swab)
>           b = swab32(b);
>
> -    writel(b, dev->base + offset);
> +    if (dev->access_16bit) {
> +        writew((u16)b, dev->base + offset);
> +        writew((u16)(b>>  16), dev->base + offset + 2);
> +    } else {
> +        writel(b, dev->base + offset);
> +    }
>   }
>
>   static u32
> @@ -258,6 +270,12 @@ int i2c_dw_init(struct dw_i2c_dev *dev)
>           reg = DW_IC_COMP_TYPE_VALUE;
>       }
>
> +    /* Configure register access mode 16bit */
> +    if (reg == (DW_IC_COMP_TYPE_VALUE&  0x0000ffff)) {

No need for a macro IMO. You are missing a space before &, though.

> +        dev->access_16bit = 1;
> +        reg = DW_IC_COMP_TYPE_VALUE;
> +    }
> +
>       if (reg != DW_IC_COMP_TYPE_VALUE) {
>           dev_err(dev->dev, "Unknown Synopsys component type: "
>               "0x%08x\n", reg);
> diff --git a/drivers/i2c/busses/i2c-designware-core.h b/drivers/i2c/busses/i2c-designware-core.h
> index 02d1a2d..f5af101 100644
> --- a/drivers/i2c/busses/i2c-designware-core.h
> +++ b/drivers/i2c/busses/i2c-designware-core.h
> @@ -83,6 +83,7 @@ struct dw_i2c_dev {
>       u32            abort_source;
>       int            irq;
>       int            swab;
> +    int            access_16bit;

This struct is already quite large. My favourite would be convert swab and access_16bit to 'unsigend accessor_flags' and proper flags. A bitfield at the end of the struct should also do.

>       struct i2c_adapter    adapter;
>       u32            functionality;
>       u32            master_cfg;


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