[PATCH v6] mfd: syscon: Decouple syscon interface from platform devices

[Heiko Stübner]

Am Montag, 29. September 2014, 14:17:38 schrieb Pankaj Dubey:
> Currently a syscon entity can be only registered directly through a
> platform device that binds to a dedicated syscon driver. However in
> certain use cases it is desirable to make a device used with another
> driver a syscon interface provider.
> 
> For example, certain SoCs (e.g. Exynos) contain system controller
> blocks which perform various functions such as power domain control,
> CPU power management, low power mode control, but in addition contain
> certain IP integration glue, such as various signal masks,
> coprocessor power control, etc. In such case, there is a need to have
> a dedicated driver for such system controller but also share registers
> with other drivers. The latter is where the syscon interface is helpful.
> 
> In case of DT based platforms, this patch decouples syscon object from
> syscon platform driver, and allows to create syscon objects first time
> when it is required by calling of syscon_regmap_lookup_by APIs and keep
> a list of such syscon objects along with syscon provider device_nodes
> and regmap handles.
> 
> For non-DT based platforms, this patch keeps syscon platform driver
> structure where is can be probed and such non-DT based drivers can use
> syscon_regmap_lookup_by_pdev API and get access to regmap handles.
> Once all users of "syscon_regmap_lookup_by_pdev" migrated to DT based,
> we can completely remove platform driver of syscon, and keep only helper
> functions to get regmap handles.
> 
> Suggested-by: Arnd Bergmann <arnd at arndb.de>
> Suggested-by: Tomasz Figa <tomasz.figa at gmail.com>
> Tested-by: Vivek Gautam <gautam.vivek at samsung.com>
> Tested-by: Javier Martinez Canillas <javier.martinez at collabora.co.uk>
> Signed-off-by: Pankaj Dubey <pankaj.dubey at samsung.com>
> ---

On Rockchip boards during core clock init (aka before timers)
Tested-by: Heiko Stuebner <heiko at sntech.de>

Except one issue described inline below
Reviewed-by: Heiko Stuebner <heiko at sntech.de>


And I'm really looking forward to having this in the kernel :-)

Thanks for working on this
Heiko


> Patch v5 and related discussions can be found here [1].
> 
> Change since v5:
>  - Dropping creation of dummy platform device in of_syscon_register.
>  - As we are changing syscon to decouple from platform_device, creation of
>    dummy platform_device does not look good option, and as suggested by
> Arnd, I made another attempt so that regmap_mmio_init API should work with
> NULL dev pointer itself. Since regmap needs to know about Syscon device
> node properties so let's parse device node of syscon in syscon itself for
> any such properties and using regmap_config parameter pass all such
> information to regmap. Other concern of crashes due to NULL dev pointer in
> regmap already addressed in separate patches of regmap. Please see [2] and
> [3].
> 
> 
> Changes since v4:
>  - Addressed Tomasz Figa's comments for v4.
>  - Added error handing in of_syscon_register function.
>  - Using devm_regmap_init_mmio instead of regmap_init_mmio.
> 
> Changes since v3:
>  - Addressed Arnd's comment for v2.
>  - Updated of_syscon_register for adding dev pointer in regmap_init_mmio.
>  - For early users created dummy platform device.
> 
> Changes since v2:
>  - Added back platform device support from syscon, with one change that
>    syscon will not be probed for DT based platform.
>  - Added back syscon_regmap_lookup_by_pdevname API so that non-DT base
>    users of syscon will not be broken.
>  - Removed unwanted change in syscon.h.
>  - Modified Signed-off-by list, added Suggested-by of Tomasz Figa and
>    Arnd Bergmann.
>  - Added Tested-by of Vivek Gautam for testing on Exynos platform.
> 
> Changes since v1:
>  - Removed of_syscon_unregister function.
>  - Modified of_syscon_register function and it will be used by syscon.c
>    to create syscon objects whenever required.
>  - Removed platform device support from syscon.
>  - Removed syscon_regmap_lookup_by_pdevname API support.
>  - As there are significant changes w.r.t patchset v1, I am taking over
>    author for this patchset from Tomasz Figa.
> 
> [1]: https://lkml.org/lkml/2014/9/22/12
> [2]: https://lkml.org/lkml/2014/9/18/130
> [3]: https://lkml.org/lkml/2014/9/27/2
> 
>  drivers/mfd/syscon.c |  106
> +++++++++++++++++++++++++++++++++++++++----------- 1 file changed, 84
> insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/mfd/syscon.c b/drivers/mfd/syscon.c
> index ca15878..00a8410 100644
> --- a/drivers/mfd/syscon.c
> +++ b/drivers/mfd/syscon.c
> @@ -15,6 +15,7 @@
>  #include <linux/err.h>
>  #include <linux/io.h>
>  #include <linux/module.h>
> +#include <linux/list.h>
>  #include <linux/of.h>
>  #include <linux/of_address.h>
>  #include <linux/of_platform.h>
> @@ -22,31 +23,104 @@
>  #include <linux/platform_device.h>
>  #include <linux/regmap.h>
>  #include <linux/mfd/syscon.h>
> +#include <linux/slab.h>
> 
>  static struct platform_driver syscon_driver;
> 
> +static DEFINE_SPINLOCK(syscon_list_slock);
> +static LIST_HEAD(syscon_list);
> +
>  struct syscon {
> +	struct device_node *np;
>  	struct regmap *regmap;
> +	struct list_head list;
> +};
> +
> +static struct regmap_config syscon_regmap_config = {
> +	.reg_bits = 32,
> +	.val_bits = 32,
> +	.reg_stride = 4,
>  };
> 
> -static int syscon_match_node(struct device *dev, void *data)
> +static struct syscon *of_syscon_register(struct device_node *np)
>  {
> -	struct device_node *dn = data;
> +	struct syscon *syscon;
> +	struct regmap *regmap;
> +	void __iomem *base;
> +	int ret;
> +	enum regmap_endian endian = REGMAP_ENDIAN_DEFAULT;
> +
> +	if (!of_device_is_compatible(np, "syscon"))
> +		return ERR_PTR(-EINVAL);
> +
> +	syscon = kzalloc(sizeof(*syscon), GFP_KERNEL);
> +	if (!syscon)
> +		return ERR_PTR(-ENOMEM);
> +
> +	base = of_iomap(np, 0);
> +	if (!base) {
> +		ret = -ENOMEM;
> +		goto err_map;
> +	}
> +
> +	/* Parse the device's DT node for an endianness specification */
> +	if (of_property_read_bool(np, "big-endian"))
> +		endian = REGMAP_ENDIAN_BIG;
> +	 else if (of_property_read_bool(np, "little-endian"))
> +		endian = REGMAP_ENDIAN_LITTLE;
> +
> +	/* If the endianness was specified in DT, use that */
> +	if (endian != REGMAP_ENDIAN_DEFAULT)
> +		syscon_regmap_config.val_format_endian = endian;
> +
> +	regmap = regmap_init_mmio(NULL, base, &syscon_regmap_config);
> +	if (IS_ERR(regmap)) {
> +		pr_err("regmap init failed\n");
> +		ret = PTR_ERR(regmap);
> +		goto err_regmap;
> +	}
> +
> +	syscon->regmap = regmap;
> +	syscon->np = np;
> +
> +	spin_lock(&syscon_list_slock);
> +	list_add_tail(&syscon->list, &syscon_list);
> +	spin_unlock(&syscon_list_slock);
> 
> -	return (dev->of_node == dn) ? 1 : 0;
> +	/* Change back endianness of syscon_regmap_config.
> +	 * As this is static config in this file and in one system we may
> +	 * have more than one syscon
> +	 */
> +	syscon_regmap_config.val_format_endian = REGMAP_ENDIAN_DEFAULT;

This should also be done in the error case. Currently when you goto err_regmap 
the overridden value will be left in the struct.

While on this, is there a concurrency issue here, aka of_syscon_register could 
be called in parallel and what happens with 
syscon_regmap_config.val_format_endian then?


> +
> +	return syscon;
> +
> +err_regmap:
> +	iounmap(base);
> +err_map:
> +	kfree(syscon);
> +	return ERR_PTR(ret);
>  }
> 
>  struct regmap *syscon_node_to_regmap(struct device_node *np)
>  {
> -	struct syscon *syscon;
> -	struct device *dev;
> +	struct syscon *entry, *syscon = NULL;
> 
> -	dev = driver_find_device(&syscon_driver.driver, NULL, np,
> -				 syscon_match_node);
> -	if (!dev)
> -		return ERR_PTR(-EPROBE_DEFER);
> +	spin_lock(&syscon_list_slock);
> 
> -	syscon = dev_get_drvdata(dev);
> +	list_for_each_entry(entry, &syscon_list, list)
> +		if (entry->np == np) {
> +			syscon = entry;
> +			break;
> +		}
> +
> +	spin_unlock(&syscon_list_slock);
> +
> +	if (!syscon)
> +		syscon = of_syscon_register(np);
> +
> +	if (IS_ERR(syscon))
> +		return ERR_CAST(syscon);
> 
>  	return syscon->regmap;
>  }
> @@ -110,17 +184,6 @@ struct regmap *syscon_regmap_lookup_by_phandle(struct
> device_node *np, }
>  EXPORT_SYMBOL_GPL(syscon_regmap_lookup_by_phandle);
> 
> -static const struct of_device_id of_syscon_match[] = {
> -	{ .compatible = "syscon", },
> -	{ },
> -};
> -
> -static struct regmap_config syscon_regmap_config = {
> -	.reg_bits = 32,
> -	.val_bits = 32,
> -	.reg_stride = 4,
> -};
> -
>  static int syscon_probe(struct platform_device *pdev)
>  {
>  	struct device *dev = &pdev->dev;
> @@ -167,7 +230,6 @@ static struct platform_driver syscon_driver = {
>  	.driver = {
>  		.name = "syscon",
>  		.owner = THIS_MODULE,
> -		.of_match_table = of_syscon_match,
>  	},
>  	.probe		= syscon_probe,
>  	.id_table	= syscon_ids,