linux-kernel - Re: [PATCH v2 3/7] firmware: raspberrypi: Provide a helper to query a clock max rate

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Date:   Mon, 10 Oct 2022 18:52:34 +0200
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Maxime Ripard <maxime@...no.tech>, Daniel Vetter <daniel@...ll.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@...adcom.com>,
        Michael Turquette <mturquette@...libre.com>,
        Scott Branden <sbranden@...adcom.com>,
        Stephen Boyd <sboyd@...nel.org>, Emma Anholt <emma@...olt.net>,
        Ray Jui <rjui@...adcom.com>, Maxime Ripard <mripard@...nel.org>
Cc:     linux-rpi-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, Dom Cobley <popcornmix@...il.com>,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 3/7] firmware: raspberrypi: Provide a helper to query a
 clock max rate

Hi Maxime,

Am 20.09.22 um 14:50 schrieb Maxime Ripard:
> The firmware allows to query for its clocks the operating range of a
> given clock. We'll need this for some drivers (KMS, in particular) to
> infer the state of some configuration options, so let's create a
> function to do so.
>
> Signed-off-by: Maxime Ripard <maxime@...no.tech>
>
> diff --git a/drivers/firmware/raspberrypi.c b/drivers/firmware/raspberrypi.c
> index b916e1e171f8..c4b9ea70f5a7 100644
> --- a/drivers/firmware/raspberrypi.c
> +++ b/drivers/firmware/raspberrypi.c
> @@ -228,6 +228,21 @@ static void rpi_register_clk_driver(struct device *dev)
>   						-1, NULL, 0);
>   }
>   
> +unsigned int rpi_firmware_clk_get_max_rate(struct rpi_firmware *fw, unsigned int id)
> +{
> +	struct rpi_firmware_clk_rate_request msg =
> +		RPI_FIRMWARE_CLK_RATE_REQUEST(id);
> +	int ret;
> +
> +	ret = rpi_firmware_property(fw, RPI_FIRMWARE_GET_MAX_CLOCK_RATE,
> +				    &msg, sizeof(msg));
> +	if (ret)
> +		return 0;
> +
> +	return le32_to_cpu(msg.rate);
> +}
> +EXPORT_SYMBOL_GPL(rpi_firmware_clk_get_max_rate);
> +
>   static void rpi_firmware_delete(struct kref *kref)
>   {
>   	struct rpi_firmware *fw = container_of(kref, struct rpi_firmware,
> diff --git a/include/soc/bcm2835/raspberrypi-firmware.h b/include/soc/bcm2835/raspberrypi-firmware.h
> index 74c7bcc1ac2a..10248c370229 100644
> --- a/include/soc/bcm2835/raspberrypi-firmware.h
> +++ b/include/soc/bcm2835/raspberrypi-firmware.h
> @@ -154,12 +154,32 @@ enum rpi_firmware_clk_id {
>   	RPI_FIRMWARE_NUM_CLK_ID,
>   };
>   
> +/**
> + * struct rpi_firmware_clk_rate_request - Firmware Request for a rate
> + * @id:	ID of the clock being queried
> + * @rate: Rate in Hertz. Set by the firmware.
> + *
> + * Used by @RPI_FIRMWARE_GET_CLOCK_RATE, @RPI_FIRMWARE_GET_CLOCK_MEASURED,
> + * @RPI_FIRMWARE_GET_MAX_CLOCK_RATE and @RPI_FIRMWARE_GET_MIN_CLOCK_RATE.
> + */
> +struct rpi_firmware_clk_rate_request {
> +	__le32 id;
> +	__le32 rate;
> +} __packed;
> +
> +#define RPI_FIRMWARE_CLK_RATE_REQUEST(_id)	\
> +	{					\
> +		.id = _id,			\
> +	}
> +
>   #if IS_ENABLED(CONFIG_RASPBERRYPI_FIRMWARE)
>   int rpi_firmware_property(struct rpi_firmware *fw,
>   			  u32 tag, void *data, size_t len);
>   int rpi_firmware_property_list(struct rpi_firmware *fw,
>   			       void *data, size_t tag_size);
>   void rpi_firmware_put(struct rpi_firmware *fw);
> +unsigned int rpi_firmware_clk_get_max_rate(struct rpi_firmware *fw,
> +					   unsigned int id);
>   struct device_node *rpi_firmware_find_node(void);
>   struct rpi_firmware *rpi_firmware_get(struct device_node *firmware_node);
>   struct rpi_firmware *devm_rpi_firmware_get(struct device *dev,
> @@ -179,6 +199,12 @@ static inline int rpi_firmware_property_list(struct rpi_firmware *fw,
>   
>   static inline void rpi_firmware_put(struct rpi_firmware *fw) { }
>   
> +static inline unsigned int rpi_firmware_clk_get_max_rate(struct rpi_firmware *fw,
> +							 unsigned int id)
> +{
> +	return UINT_MAX;
In case the driver is disabled the function return UINT_MAX, but in case 
the firmware doesn't support RPI_FIRMWARE_GET_MAX_CLOCK_RATE it returns 
0. This looks a little bit inconsistent to me.
> +}
> +
>   static inline struct device_node *rpi_firmware_find_node(void)
>   {
>   	return NULL;
>