Re: [PATCH 04/10] mmc: Add invert flag for clock phase signedness

Andrew Jeffery
2021-10-26T00:53:11Z

On Wed, 22 Sep 2021, at 20:01, Chin-Ting Kuo wrote:
> The clock phase degree may be between -360 to 360.
> If the data signal is leading to the clock, the signedness
> of clock phase is postive, otherwise, the signedness
> is negative.
>
> Signed-off-by: Chin-Ting Kuo <chin-ting_kuo@aspeedtech.com>

The implementation here can't be changed without a change to the
binding documentation:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/mmc/mmc-controller.yaml?h=v5.15-rc7#n345

> ---
> drivers/mmc/core/host.c | 10 ++++++----
> include/linux/mmc/host.h | 2 ++
> 2 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
> index d4683b1d263f..c2de7cbc7838 100644
> --- a/drivers/mmc/core/host.c
> +++ b/drivers/mmc/core/host.c
> @@ -214,14 +214,16 @@ static void mmc_retune_timer(struct timer_list *t)
> static void mmc_of_parse_timing_phase(struct device *dev, const char *prop,
> struct mmc_clk_phase *phase)
> {
> - int degrees[2] = {0};
> + int degrees[4] = {0};
> int rc;
>
> - rc = device_property_read_u32_array(dev, prop, degrees, 2);
> + rc = device_property_read_u32_array(dev, prop, degrees, 4);
> phase->valid = !rc;
> if (phase->valid) {
> - phase->in_deg = degrees[0];
> - phase->out_deg = degrees[1];
> + phase->inv_in_deg = degrees[0] ? true : false;
> + phase->in_deg = degrees[1];
> + phase->inv_out_deg = degrees[2] ? true : false;
> + phase->out_deg = degrees[3];

This fundamentally breaks any in-tree users. We can't do this.

In terms of the binding, if negative phase values are something we must
do, we can just extend the value range to include [-359, -1] right?
That avoids changing the type of the value positions in the manner this
patch does.

Andrew