Re: [PATCH v6 1/7] media: V4L2: add temporary clock helpers

[Sylwester Nawrocki <sylvester.nawrocki@gmail.com>]

Hi Guennadi,

On 03/15/2013 10:27 PM, Guennadi Liakhovetski wrote:
> Typical video devices like camera sensors require an external clock source.
> Many such devices cannot even access their hardware registers without a
> running clock. These clock sources should be controlled by their consumers.
> This should be performed, using the generic clock framework. Unfortunately
> so far only very few systems have been ported to that framework. This patch

It seems there is much more significant progress in adding CCF support to
various platforms than with our temporary clocks API ;)

$ git show linux-next/master:drivers/clk/Makefile
...
# SoCs specific
obj-$(CONFIG_ARCH_BCM2835)      += clk-bcm2835.o
obj-$(CONFIG_ARCH_NOMADIK)      += clk-nomadik.o
obj-$(CONFIG_ARCH_HIGHBANK)     += clk-highbank.o
obj-$(CONFIG_ARCH_MXS)          += mxs/
obj-$(CONFIG_ARCH_SOCFPGA)      += socfpga/
obj-$(CONFIG_PLAT_SPEAR)        += spear/
obj-$(CONFIG_ARCH_U300)         += clk-u300.o
obj-$(CONFIG_COMMON_CLK_VERSATILE) += versatile/
obj-$(CONFIG_ARCH_PRIMA2)       += clk-prima2.o
obj-$(CONFIG_PLAT_ORION)        += mvebu/
ifeq ($(CONFIG_COMMON_CLK), y)
obj-$(CONFIG_ARCH_MMP)          += mmp/
endif
obj-$(CONFIG_MACH_LOONGSON1)    += clk-ls1x.o
obj-$(CONFIG_ARCH_U8500)        += ux500/
obj-$(CONFIG_ARCH_VT8500)       += clk-vt8500.o
obj-$(CONFIG_ARCH_ZYNQ)         += clk-zynq.o
obj-$(CONFIG_ARCH_TEGRA)        += tegra/
obj-$(CONFIG_PLAT_SAMSUNG)      += samsung/

obj-$(CONFIG_X86)               += x86/

# Chip specific
obj-$(CONFIG_COMMON_CLK_WM831X) += clk-wm831x.o
obj-$(CONFIG_COMMON_CLK_MAX77686) += clk-max77686.o
obj-$(CONFIG_CLK_TWL6040)       += clk-twl6040.o


> adds a set of temporary helpers, mimicking the generic clock API, to V4L2.
> Platforms, adopting the clock API, should switch to using it. Eventually
> this temporary API should be removed.
>
> Signed-off-by: Guennadi Liakhovetski<g.liakhovetski@gmx.de>
> ---
>
> v6: changed clock name to just<I2C adapter ID>-<I2C address>  to avoid
> having to wait for an I2C subdevice driver to probe. Added a subdevice
> pointer to struct v4l2_clk for subdevice and bridge binding.
>
>   drivers/media/v4l2-core/Makefile   |    2 +-
>   drivers/media/v4l2-core/v4l2-clk.c |  184 ++++++++++++++++++++++++++++++++++++
>   include/media/v4l2-clk.h           |   55 +++++++++++
>   3 files changed, 240 insertions(+), 1 deletions(-)
>   create mode 100644 drivers/media/v4l2-core/v4l2-clk.c
>   create mode 100644 include/media/v4l2-clk.h
>
> diff --git a/drivers/media/v4l2-core/Makefile b/drivers/media/v4l2-core/Makefile
> index a9d3552..aea7aea 100644
> --- a/drivers/media/v4l2-core/Makefile
> +++ b/drivers/media/v4l2-core/Makefile
> @@ -5,7 +5,7 @@
>   tuner-objs	:=	tuner-core.o
>
>   videodev-objs	:=	v4l2-dev.o v4l2-ioctl.o v4l2-device.o v4l2-fh.o \
> -			v4l2-event.o v4l2-ctrls.o v4l2-subdev.o
> +			v4l2-event.o v4l2-ctrls.o v4l2-subdev.o v4l2-clk.o
>   ifeq ($(CONFIG_COMPAT),y)
>     videodev-objs += v4l2-compat-ioctl32.o
>   endif
> diff --git a/drivers/media/v4l2-core/v4l2-clk.c b/drivers/media/v4l2-core/v4l2-clk.c
> new file mode 100644
> index 0000000..3505972
> --- /dev/null
> +++ b/drivers/media/v4l2-core/v4l2-clk.c
> @@ -0,0 +1,184 @@
> +/*
> + * V4L2 clock service
> + *
> + * Copyright (C) 2012, Guennadi Liakhovetski<g.liakhovetski@gmx.de>

2013 ?

> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +
> +#include<linux/atomic.h>
> +#include<linux/errno.h>
> +#include<linux/list.h>
> +#include<linux/module.h>
> +#include<linux/mutex.h>
> +#include<linux/string.h>
> +
> +#include<media/v4l2-clk.h>
> +#include<media/v4l2-subdev.h>
> +
> +static DEFINE_MUTEX(clk_lock);
> +static LIST_HEAD(clk_list);
> +
> +static struct v4l2_clk *v4l2_clk_find(const struct v4l2_subdev *sd,
> +				      const char *dev_id, const char *id)
> +{
> +	struct v4l2_clk *clk;
> +
> +	list_for_each_entry(clk,&clk_list, list) {
> +		if (!sd || !(sd->flags&  V4L2_SUBDEV_FL_IS_I2C)) {
> +			if (strcmp(dev_id, clk->dev_id))
> +				continue;
> +		} else {
> +			char *i2c = strstr(dev_id, clk->dev_id);
> +			if (!i2c || i2c = dev_id || *(i2c - 1) != ' ')
> +				continue;
> +		}
> +
> +		if (!id || !clk->id || !strcmp(clk->id, id))
> +			return clk;
> +	}
> +
> +	return ERR_PTR(-ENODEV);
> +}
> +
> +struct v4l2_clk *v4l2_clk_get(struct v4l2_subdev *sd, const char *id)
> +{
> +	struct v4l2_clk *clk;
> +
> +	mutex_lock(&clk_lock);
> +	clk = v4l2_clk_find(sd, sd->name, id);

Couldn't we just pass the I2C client's struct device name to this function ?
And if the host driver that registers a clock for its sub-device knows 
the type
of device (I2C, SPI client, etc.) why we need to even bother with 
checking the
subdev/bus type in v4l2_clk_find() function above, when the host could 
properly
format dev_id when it registers a clock ? Then the subdev would just 
pass its
struct device pointer to this API to find its clock. What am I missing 
here ?

> +	if (!IS_ERR(clk)&&  !try_module_get(clk->ops->owner))
> +		clk = ERR_PTR(-ENODEV);
> +	mutex_unlock(&clk_lock);
> +
> +	if (!IS_ERR(clk)) {
> +		clk->subdev = sd;

Why is this needed ? It seems a strange addition that might potentially
make transition to the common clocks API more difficult.

> +		atomic_inc(&clk->use_count);
> +	}
> +
> +	return clk;
> +}
> +EXPORT_SYMBOL(v4l2_clk_get);
> +
[...]
> +unsigned long v4l2_clk_get_rate(struct v4l2_clk *clk)
> +{
> +	if (!clk->ops->get_rate)
> +		return -ENOSYS;

I guess we should just WARN if this callback is null and return 0
or return value type of this function needs to be 'long'. Otherwise
we'll get insanely large frequency value by casting this error code
to unsigned long.

> +
> +	return clk->ops->get_rate(clk);
> +}
> +EXPORT_SYMBOL(v4l2_clk_get_rate);
> +
> +int v4l2_clk_set_rate(struct v4l2_clk *clk, unsigned long rate)
> +{
> +	if (!clk->ops->set_rate)
> +		return -ENOSYS;
> +
> +	return clk->ops->set_rate(clk, rate);
> +}
> +EXPORT_SYMBOL(v4l2_clk_set_rate);
> +
> +struct v4l2_clk *v4l2_clk_register(const struct v4l2_clk_ops *ops,
> +				   const char *dev_id,
> +				   const char *id, void *priv)
> +{
> +	struct v4l2_clk *clk;
> +	int ret;
> +
> +	if (!ops || !dev_id)
> +		return ERR_PTR(-EINVAL);
> +
> +	clk = kzalloc(sizeof(struct v4l2_clk), GFP_KERNEL);
> +	if (!clk)
> +		return ERR_PTR(-ENOMEM);
> +
> +	clk->id = kstrdup(id, GFP_KERNEL);
> +	clk->dev_id = kstrdup(dev_id, GFP_KERNEL);
> +	if ((id&&  !clk->id) || !clk->dev_id) {
> +		ret = -ENOMEM;
> +		goto ealloc;
> +	}
> +	clk->ops = ops;
> +	clk->priv = priv;
> +	atomic_set(&clk->use_count, 0);
> +	mutex_init(&clk->lock);
> +
> +	mutex_lock(&clk_lock);
> +	if (!IS_ERR(v4l2_clk_find(NULL, dev_id, id))) {
> +		mutex_unlock(&clk_lock);
> +		ret = -EEXIST;
> +		goto eexist;
> +	}
> +	list_add_tail(&clk->list,&clk_list);
> +	mutex_unlock(&clk_lock);
> +
> +	return clk;
> +
> +eexist:
> +ealloc:

nit: Why not to make the label's name dependant on what code follows
a label and avoid this double labelling ? In general it seems a good
idea to name the label after where we jump to, not where we start from.

> +	kfree(clk->id);
> +	kfree(clk->dev_id);
> +	kfree(clk);
> +	return ERR_PTR(ret);
> +}
> +EXPORT_SYMBOL(v4l2_clk_register);

--

Regards,
Sylwester