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Message-ID: <f467e4a8-fcb2-4345-b8f7-7557c1a7552b@redhat.com>
Date: Sat, 10 May 2025 16:21:09 +0200
From: Hans de Goede <hdegoede@...hat.com>
To: Mehdi Djait <mehdi.djait@...ux.intel.com>, sakari.ailus@...ux.intel.com,
laurent.pinchart@...asonboard.com
Cc: tomi.valkeinen@...asonboard.com, jacopo.mondi@...asonboard.com,
hverkuil@...all.nl, kieran.bingham@...asonboard.com, naush@...pberrypi.com,
mchehab@...nel.org, dave.stevenson@...pberrypi.com,
linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v4] media: v4l2-common: Add a helper for obtaining the
clock producer
Hi Mehdi,
On 21-Mar-25 2:03 PM, Mehdi Djait wrote:
> Introduce a helper for v4l2 sensor drivers on both DT- and ACPI-based
> platforms to retrieve a reference to the clock producer from firmware.
>
> This helper behaves the same as clk_get_optional() except where there is
> no clock producer like in ACPI-based platforms.
>
> For ACPI-based platforms the function will read the "clock-frequency"
> ACPI _DSD property and register a fixed frequency clock with the frequency
> indicated in the property.
>
> Signed-off-by: Mehdi Djait <mehdi.djait@...ux.intel.com>
This certainly looks quite useful, thank you for working
on this.
Note on some IPU3 platforms where the clk is provided by
a clk-generator which is part of a special sensor-PMIC
the situation is a bit more complicated.
Basically if there is both a clk provider and a clock-frequency
property then the clock-frequency value should be set as freq
to the clk-provider, see:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/media/i2c/ov8865.c#n3020
for an example of a driver which handles this case.
IMHO it would be good if the generic helper would handle
this case too and if there is both a clk-provider and
a clock-frequency property then try to set the clock-frequency
value with clk_set_rate(), arguably you could just warn on
a failure to set the rate though, instead of the error
the ov8865 driver currently throws.
Sakari, Laurent any opinions on adding handling this case
to the generic helper ?
Regards,
Hans
> ---
> v1 -> v2:
> Suggested by Sakari:
> - removed clk_name
> - removed the IS_ERR() check
> - improved the kernel-doc comment and commit msg
> Link v1: https://lore.kernel.org/linux-media/20250227092643.113939-1-mehdi.djait@linux.intel.com
>
> v2 -> v3:
> - Added #ifdef CONFIG_COMMON_CLK for the ACPI case
> Link v2: https://lore.kernel.org/linux-media/20250310122305.209534-1-mehdi.djait@linux.intel.com/
>
> v3 -> v4:
> Suggested by Laurent:
> - removed the #ifdef to use IS_REACHABLE(CONFIG_COMMON_CLK)
> - changed to kasprintf() to allocate the clk name when id is NULL and
> used the __free(kfree) scope-based cleanup helper when
> defining the variable to hold the allocated name
> Link v3: https://lore.kernel.org/linux-media/20250321093814.18159-1-mehdi.djait@linux.intel.com/
>
>
> drivers/media/v4l2-core/v4l2-common.c | 40 +++++++++++++++++++++++++++
> include/media/v4l2-common.h | 18 ++++++++++++
> 2 files changed, 58 insertions(+)
>
> diff --git a/drivers/media/v4l2-core/v4l2-common.c b/drivers/media/v4l2-core/v4l2-common.c
> index 0a2f4f0d0a07..b33152e2c3af 100644
> --- a/drivers/media/v4l2-core/v4l2-common.c
> +++ b/drivers/media/v4l2-core/v4l2-common.c
> @@ -34,6 +34,9 @@
> * Added Gerd Knorrs v4l1 enhancements (Justin Schoeman)
> */
>
> +#include <linux/clk.h>
> +#include <linux/clkdev.h>
> +#include <linux/clk-provider.h>
> #include <linux/module.h>
> #include <linux/types.h>
> #include <linux/kernel.h>
> @@ -636,3 +639,40 @@ int v4l2_link_freq_to_bitmap(struct device *dev, const u64 *fw_link_freqs,
> return 0;
> }
> EXPORT_SYMBOL_GPL(v4l2_link_freq_to_bitmap);
> +
> +struct clk *devm_v4l2_sensor_clk_get(struct device *dev, const char *id)
> +{
> + const char *clk_id __free(kfree) = NULL;
> + struct clk_hw *clk_hw;
> + struct clk *clk;
> + u32 rate;
> + int ret;
> +
> + clk = devm_clk_get_optional(dev, id);
> + if (clk)
> + return clk;
> +
> + if (!IS_REACHABLE(CONFIG_COMMON_CLK))
> + return ERR_PTR(-ENOENT);
> +
> + if (!is_acpi_node(dev_fwnode(dev)))
> + return ERR_PTR(-ENOENT);
> +
> + ret = device_property_read_u32(dev, "clock-frequency", &rate);
> + if (ret)
> + return ERR_PTR(ret);
> +
> + if (!id) {
> + clk_id = kasprintf(GFP_KERNEL, "clk-%s", dev_name(dev));
> + if (!clk_id)
> + return ERR_PTR(-ENOMEM);
> + id = clk_id;
> + }
> +
> + clk_hw = devm_clk_hw_register_fixed_rate(dev, id, NULL, 0, rate);
> + if (IS_ERR(clk_hw))
> + return ERR_CAST(clk_hw);
> +
> + return clk_hw->clk;
> +}
> +EXPORT_SYMBOL_GPL(devm_v4l2_sensor_clk_get);
> diff --git a/include/media/v4l2-common.h b/include/media/v4l2-common.h
> index 63ad36f04f72..35b9ac698e8a 100644
> --- a/include/media/v4l2-common.h
> +++ b/include/media/v4l2-common.h
> @@ -573,6 +573,24 @@ int v4l2_link_freq_to_bitmap(struct device *dev, const u64 *fw_link_freqs,
> unsigned int num_of_driver_link_freqs,
> unsigned long *bitmap);
>
> +/**
> + * devm_v4l2_sensor_clk_get - lookup and obtain a reference to an optional clock
> + * producer for a camera sensor.
> + *
> + * @dev: device for v4l2 sensor clock "consumer"
> + * @id: clock consumer ID
> + *
> + * This function behaves the same way as clk_get_optional() except where there
> + * is no clock producer like in ACPI-based platforms.
> + * For ACPI-based platforms, the function will read the "clock-frequency"
> + * ACPI _DSD property and register a fixed-clock with the frequency indicated
> + * in the property.
> + *
> + * Return:
> + * * pointer to a struct clk on success or an error code on failure.
> + */
> +struct clk *devm_v4l2_sensor_clk_get(struct device *dev, const char *id);
> +
> static inline u64 v4l2_buffer_get_timestamp(const struct v4l2_buffer *buf)
> {
> /*
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