Re: [PATCH RFT] spi: sc18is602: Convert to let spi core validate transfer speed

[Guenter Roeck <linux-0h96xk9xTtrk1uMJSBkQmQ@public.gmane.org>]

On 02/28/2014 02:39 AM, Axel Lin wrote:
> Set master->max_speed_hz and master->min_speed_hz then spi core will handle
> checking transfer speed. So we can remove the same checking in this driver.
>
> This patch also remove testing if hz is 0 because spi->max_speed_hz will be
> default set to master->min_speed_hz if it was not set. So the transfer speed
> will never set to 0.
>
> Signed-off-by: Axel Lin <axel.lin-8E1dMatC8ynQT0dZR+AlfA@public.gmane.org>
> ---
>   drivers/spi/spi-sc18is602.c | 13 +++----------
>   1 file changed, 3 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/spi/spi-sc18is602.c b/drivers/spi/spi-sc18is602.c
> index 7fba10b..237f2e7 100644
> --- a/drivers/spi/spi-sc18is602.c
> +++ b/drivers/spi/spi-sc18is602.c
> @@ -183,17 +183,9 @@ static int sc18is602_setup_transfer(struct sc18is602 *hw, u32 hz, u8 mode)
>   static int sc18is602_check_transfer(struct spi_device *spi,
>   				    struct spi_transfer *t, int tlen)
>   {
> -	uint32_t hz;
> -
>   	if (t && t->len + tlen > SC18IS602_BUFSIZ)
>   		return -EINVAL;
>
> -	hz = spi->max_speed_hz;
> -	if (t && t->speed_hz)
> -		hz = t->speed_hz;
> -	if (hz == 0)
> -		return -EINVAL;
> -
>   	return 0;
>   }
>
> @@ -207,14 +199,13 @@ static int sc18is602_transfer_one(struct spi_master *master,
>
>   	hw->tlen = 0;
>   	list_for_each_entry(t, &m->transfers, transfer_list) {
> -		u32 hz = t->speed_hz ? : spi->max_speed_hz;
>   		bool do_transfer;
>
>   		status = sc18is602_check_transfer(spi, t, hw->tlen);
>   		if (status < 0)
>   			break;
>
> -		status = sc18is602_setup_transfer(hw, hz, spi->mode);
> +		status = sc18is602_setup_transfer(hw, t->speed_hz, spi->mode);
>   		if (status < 0)
>   			break;
>
> @@ -305,6 +296,8 @@ static int sc18is602_probe(struct i2c_client *client,
>   	master->setup = sc18is602_setup;
>   	master->transfer_one_message = sc18is602_transfer_one;
>   	master->dev.of_node = np;
> +	master->min_speed_hz = hw->freq / 128;
> +	master->max_speed_hz = hw->freq / 4;
>

Turns out this results in a failure if the requested speed is higher than
the supported speed. Previous code would simply update the speed to the
maximum supported speed.

Since the patch was already accepted, I'll send a follow-up patch to make
this less restrictive; I don't see the need to reject a transfer request
at 2mbps because the chip can only support 1.843 mbps.

Guenter

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