linux-kernel - Re: [PATCH v2 2/8] pinctrl: stm32: Introduce HDP driver

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Message-ID: <CACRpkdZp6D-duzyVRLv5+PURb3Nu69njJx_33D-2aYS4DjmsoQ@mail.gmail.com>
Date: Wed, 21 May 2025 00:34:48 +0200
From: Linus Walleij <linus.walleij@...aro.org>
To: Clément Le Goffic <clement.legoffic@...s.st.com>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, Maxime Coquelin <mcoquelin.stm32@...il.com>, 
	Alexandre Torgue <alexandre.torgue@...s.st.com>, Bartosz Golaszewski <brgl@...ev.pl>, 
	linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com, 
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 2/8] pinctrl: stm32: Introduce HDP driver

Hi Clément,

thanks for your patch!

On Tue, May 20, 2025 at 5:04 PM Clément Le Goffic
<clement.legoffic@...s.st.com> wrote:

> This patch introduce the driver for the Hardware Debug Port available on
> STM32MP platforms. The HDP allows the observation of internal SoC
> signals by using multiplexers. Each HDP port can provide up to 16
> internal signals (one of them can be software controlled as a GPO).
>
> Signed-off-by: Clément Le Goffic <clement.legoffic@...s.st.com>

(...)
> +static int stm32_hdp_gpio_get_direction(struct gpio_chip *gc, unsigned int offset)
> +{
> +       return GPIO_LINE_DIRECTION_OUT;
> +}

That's reasonable.

> +static int stm32_hdp_gpio_get(struct gpio_chip *gc, unsigned int offset)
> +{
> +       struct stm32_hdp *hdp = gpiochip_get_data(gc);
> +
> +       if (((hdp->mux_conf & HDP_MUX_MASK(offset))) == HDP_MUX_GPOVAL(offset))
> +               return !!(readl_relaxed(hdp->base + HDP_GPOVAL) & BIT(offset));
> +       else
> +               return !!(readl_relaxed(hdp->base + HDP_VAL) & BIT(offset));
> +}

...but you still make it possible to read the value of the line
if it's not muxed as GPO?

Should it not stm32_hdp_gpio_get_direction() return
GPIO_LINE_DIRECTION_IN if HDP_MUX_MASK(offset))) != HDP_MUX_GPOVAL(offset)?

> +static void stm32_hdp_gpio_set(struct gpio_chip *gc, unsigned int offset, int value)
> +{
> +       struct stm32_hdp *hdp = gpiochip_get_data(gc);
> +
> +       if (value)
> +               writel_relaxed(BIT(offset), hdp->base + HDP_GPOSET);
> +       else
> +               writel_relaxed(BIT(offset), hdp->base + HDP_GPOCLR);
> +}

Can't you just use GPIO_GENERIC for this?

bgpio_init(gc, dev, ARRAY_SIZE(stm32_hdp_pins), // == 8
    hdp->base + HDP_VAL,
    hdp->base + HDP_GPOSET,
    hdp->base + HDP_GPOCLR,
    NULL,
    NULL,
    0);

The default behaviour of GPIO MMIO is to read the output register
for the value if the line is in output mode.

You may wanna override the .get_direction() callback after bgpio_init()
and before registering the chip, either with what you have or what
I described above.

Yours,
Linus Walleij