linux-kernel - Re: [PATCH 1/8] pinctrl: aspeed: "Not enabled" is a significant mux state

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Message-ID: <CACPK8XcWuZe9bCLAwX+FGvEjgMqQmEhGAR1V65hvCmKuTa-s7Q@mail.gmail.com>
Date:   Thu, 29 Sep 2016 10:24:09 +0930
From:   Joel Stanley <joel@....id.au>
To:     Andrew Jeffery <andrew@...id.au>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh+dt@...nel.org>, linux-gpio@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org,
        OpenBMC Maillist <openbmc@...ts.ozlabs.org>
Subject: Re: [PATCH 1/8] pinctrl: aspeed: "Not enabled" is a significant mux state

On Wed, Sep 28, 2016 at 12:20 AM, Andrew Jeffery <andrew@...id.au> wrote:
> Consider a scenario with one pin P that has two signals A and B, where A
> is defined to be higher priority than B: That is, if the mux IP is in a
> state that would consider both A and B to be active on P, then A will be
> the active signal.
>
> To instead configure B as the active signal we must configure the mux so
> that A is inactive. The mux state for signals can be described by
> logical operations on one or more bits from one or more registers (a
> "signal expression"), which in some cases leads to aliased mux states for
> a particular signal. Further, signals described by multi-bit bitfields
> often do not only need to record the states that would make them active
> (the "enable" expressions), but also the states that makes them inactive
> (the "disable" expressions). All of this combined leads to four possible
> states for a signal:
>
>          1. A signal is active with respect to an "enable" expression
>          2. A signal is not active with respect to an "enable" expression
>          3. A signal is inactive with respect to a "disable" expression
>          4. A signal is not inactive with respect to a "disable" expression
>
> In the case of P, if we are looking to activate B without explicitly
> having configured A it's enough to consider A inactive if all of A's
> "enable" signal expressions evaluate to "not active". If any evaluate to
> "active" then the corresponding "disable" states must be applied so it
> becomes inactive.
>
> For example, on the AST2400 the pins composing GPIO bank H provide
> signals ROMD8 through ROMD15 (high priority) and those for UART6 (low
> priority). The mux states for ROMD8 through ROMD15 are aliased, i.e.
> there are two mux states that result in the respective signals being
> configured:
>
>          A. SCU90[6]=1
>          B. Strap[4,1:0]=100
>
> Further, the second mux state is a 3-bit bitfield that explicitly
> defines the enabled state but the disabled state is implicit, i.e. if
> Strap[4,1:0] is not exactly "100" then ROMD8 through ROMD15 are not
> considered active. This requires the mux function evaluation logic to
> use approach 2. above, however the existing code was using approach 3.
> The problem was brought to light on the Palmetto machines where the
> strap register value is 0x120ce416, and prevented GPIO requests in bank
> H from succeeding despite the hardware being in a position to allow
> them.
>
> Fixes: 318398c09a8d ("pinctrl: Add core pinctrl support for Aspeed SoCs")
> Signed-off-by: Andrew Jeffery <andrew@...id.au>

That's a decent commit message.

Reviewed-by: Joel Stanley <joel@....id.au>

> ---
>  drivers/pinctrl/aspeed/pinctrl-aspeed.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/pinctrl/aspeed/pinctrl-aspeed.c b/drivers/pinctrl/aspeed/pinctrl-aspeed.c
> index 0391f9f13f3e..49aeba912531 100644
> --- a/drivers/pinctrl/aspeed/pinctrl-aspeed.c
> +++ b/drivers/pinctrl/aspeed/pinctrl-aspeed.c
> @@ -166,13 +166,9 @@ static bool aspeed_sig_expr_set(const struct aspeed_sig_expr *expr,
>                                 bool enable, struct regmap *map)
>  {
>         int i;
> -       bool ret;
> -
> -       ret = aspeed_sig_expr_eval(expr, enable, map);
> -       if (ret)
> -               return ret;
>
>         for (i = 0; i < expr->ndescs; i++) {
> +               bool ret;
>                 const struct aspeed_sig_desc *desc = &expr->descs[i];
>                 u32 pattern = enable ? desc->enable : desc->disable;
>
> @@ -199,12 +195,18 @@ static bool aspeed_sig_expr_set(const struct aspeed_sig_expr *expr,
>  static bool aspeed_sig_expr_enable(const struct aspeed_sig_expr *expr,
>                                    struct regmap *map)
>  {
> +       if (aspeed_sig_expr_eval(expr, true, map))
> +               return true;
> +
>         return aspeed_sig_expr_set(expr, true, map);
>  }
>
>  static bool aspeed_sig_expr_disable(const struct aspeed_sig_expr *expr,
>                                     struct regmap *map)
>  {
> +       if (!aspeed_sig_expr_eval(expr, true, map))
> +               return true;
> +
>         return aspeed_sig_expr_set(expr, false, map);
>  }
>
> --
> git-series 0.8.10