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

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Date:   Tue, 26 Oct 2021 11:22:49 +1030
From:   "Andrew Jeffery" <andrew@...id.au>
To:     "Chin-Ting Kuo" <chin-ting_kuo@...eedtech.com>,
        "Rob Herring" <robh+dt@...nel.org>,
        "Joel Stanley" <joel@....id.au>,
        "Michael Turquette" <mturquette@...libre.com>,
        "Stephen Boyd" <sboyd@...nel.org>,
        "Adrian Hunter" <adrian.hunter@...el.com>,
        linux-aspeed@...ts.ozlabs.org, openbmc@...ts.ozlabs.org,
        linux-mmc <linux-mmc@...r.kernel.org>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org
Cc:     BMC-SW@...eedtech.com, "Steven Lee" <steven_lee@...eedtech.com>
Subject: Re: [PATCH 04/10] mmc: Add invert flag for clock phase signedness

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@...eedtech.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