Date:	Tue, 15 Jul 2014 12:27:13 +0300
From:	Stanimir Varbanov <svarbanov@...sol.com>
To:	Lee Jones <lee.jones@...aro.org>
CC:	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, Rob Herring <robh@...nel.org>,
	Kumar Gala <galak@...eaurora.org>,
	Grant Likely <grant.likely@...aro.org>,
	Courtney Cavin <courtney.cavin@...ymobile.com>,
	Josh Cartwright <joshc@...eaurora.org>
Subject: Re: [RFC PATCH v2 1/5] mfd: qpnp: add support for Qualcomm QPNP PMICs

On 07/14/2014 05:03 PM, Lee Jones wrote:
> On Mon, 14 Jul 2014, Stanimir Varbanov wrote:
>> On 07/11/2014 12:07 PM, Lee Jones wrote:
>>> On Thu, 10 Jul 2014, Stanimir Varbanov wrote:
>>>>>>>> The Qualcomm QPNP PMIC chips are components used with the
>>>>>>>> Snapdragon 800 series SoC family.  This driver exists
>>>>>>>> largely as a glue mfd component, it exists to be an owner
>>>>>>>> of an SPMI regmap for children devices described in
>>>>>>>> device tree.
>>>>>>>>
>>>>>>>> Signed-off-by: Josh Cartwright <joshc@...eaurora.org>
>>>>>>>> Signed-off-by: Stanimir Varbanov <svarbanov@...sol.com>
>>>>>>>> ---
>>>>>>>>  drivers/mfd/Kconfig     |   15 ++++++
>>>>>>>>  drivers/mfd/Makefile    |    1 +
>>>>>>>>  drivers/mfd/qpnp-spmi.c |  129 +++++++++++++++++++++++++++++++++++++++++++++++
>>>>>>>>  3 files changed, 145 insertions(+), 0 deletions(-)
>>>>>>>>  create mode 100644 drivers/mfd/qpnp-spmi.c
>>>>>>>>
>>>>>>>> diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
>>>>>>>> index ee8204c..258b733 100644
>>>>>>>> --- a/drivers/mfd/Kconfig
>>>>>>>> +++ b/drivers/mfd/Kconfig
>>>>>>>> @@ -524,6 +524,21 @@ config MFD_PM8921_CORE
>>>>>>>>  	  Say M here if you want to include support for PM8921 chip as a module.
>>>>>>>>  	  This will build a module called "pm8921-core".
>>>>>>>>  
>>>>>>>> +config MFD_QPNP_SPMI
>>>>>>>> +	tristate "Qualcomm QPNP SPMI PMIC"
>>>>>>>> +	depends on ARCH_QCOM || COMPILE_TEST
>>>>>>>> +	depends on OF
>>>>>>>> +	select MFD_CORE
>>>>>>>> +	select REGMAP_SPMI
>>>>>>>> +	help
>>>>>>>> +	  This enables support for the Qualcomm QPNP SPMI PMICs.
>>>>>>>> +	  These PMICs are currently used with the Snapdragon 800 series of
>>>>>>>> +	  SoCs.  Note, that this will only be useful paired with descriptions
>>>>>>>> +	  of the independent functions as children nodes in the device tree.
>>>>>>>
>>>>
>>>> <snip>
>>>>
>>>>>>>
>>>>>>>> + * This program is distributed in the hope that it will be useful,
>>>>>>>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>>>>>>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>>>>>>>> + * GNU General Public License for more details.
>>>>>>>> + */
>>>>>>>> +#include <linux/kernel.h>
>>>>>>>> +#include <linux/module.h>
>>>>>>>> +#include <linux/spmi.h>
>>>>>>>> +#include <linux/regmap.h>
>>>>>>>> +#include <linux/of_address.h>
>>>>>>>> +#include <linux/slab.h>
>>>>>>>> +#include <linux/mfd/core.h>
>>>>>>>> +
>>>>>>>> +#define QPNP_RESOURCE_SIZE	256
>>>>>>>> +
>>>>>>>> +static const struct regmap_config qpnp_regmap_config = {
>>>>>>>> +	.reg_bits	= 16,
>>>>>>>> +	.val_bits	= 8,
>>>>>>>> +	.max_register	= 0xffff,
>>>>>>>> +};
>>>>>>>> +
>>>>>>>> +static int qpnp_index_to_resource(struct device_node *np, int index,
>>>>>>>> +				  struct resource *res)
>>>>>>>> +{
>>>>>>>> +	const char *name = NULL;
>>>>>>>> +	const __be32 *addrp;
>>>>>>>> +	u64 addr;
>>>>>>>> +
>>>>>>>> +	addrp = of_get_address(np, index, NULL, NULL);
>>>>>>>> +	if (!addrp)
>>>>>>>> +		return -EINVAL;
>>>>>>>> +
>>>>>>>> +	addr = of_read_number(addrp, 1);
>>>>>>>> +	if (addr == OF_BAD_ADDR)
>>>>>>>> +		return -EINVAL;
>>>>>>>> +
>>>>>>>> +	of_property_read_string_index(np, "reg-names", index, &name);
>>>>>>>> +
>>>>>>>> +	res->start = addr;
>>>>>>>> +	res->end = addr + QPNP_RESOURCE_SIZE - 1;
>>>>>>>> +	res->flags = IORESOURCE_REG;
>>>>>>>> +	res->name = name ? name : np->name;
>>>>>>>> +
>>>>>>>> +	return 0;
>>>>>>>> +}
>>>>>>>> +
>>>>>>>> +static int qpnp_add_device(struct spmi_device *root, struct device_node *child)
>>>>>>>> +{
>>>>>>>> +	struct mfd_cell cell = {};
>>>>>>>> +	struct resource *res, *r;
>>>>>>>> +	int num_resources = 0;
>>>>>>>> +	const char *compat;
>>>>>>>> +	int ret, i;
>>>>>>>> +
>>>>>>>> +	compat = of_get_property(child, "compatible", NULL);
>>>>>>>> +	if (!compat)
>>>>>>>> +		return -ENODEV;
>>>>>>>> +
>>>>>>>> +	while (of_get_address(child, num_resources, NULL, NULL))
>>>>>>>> +		num_resources++;
>>>>>>>> +
>>>>>>>> +	if (!num_resources)
>>>>>>>> +		return -ENODEV;
>>>>>>>> +
>>>>>>>> +	res = kcalloc(num_resources, sizeof(*res), GFP_KERNEL);
>>>>>>>> +	if (!res)
>>>>>>>> +		return -ENOMEM;
>>>>>>>> +
>>>>>>>> +	r = res;
>>>>>>>> +	for (i = 0; i < num_resources; i++, r++)
>>>>>>>> +		qpnp_index_to_resource(child, i, r);
>>>>>>>> +
>>>>>>>> +	cell.name = kasprintf(GFP_KERNEL, "%x.%04x.%s", root->usid,
>>>>>>>> +			      (u16)res[0].start, child->name);
>>>>>>>> +	cell.of_compatible = compat;
>>>>>>>> +	cell.num_resources = num_resources;
>>>>>>>> +	cell.resources = res;
>>>>>>>> +
>>>>>>>> +	ret = mfd_add_devices(&root->dev, PLATFORM_DEVID_NONE, &cell, 1,
>>>>>>>> +			      NULL, 0, NULL);
>>>>>>>> +
>>>>>>>> +	kfree(res);
>>>>>>>> +	kfree(cell.name);
>>>>>>>> +
>>>>>>>> +	return ret;
>>>>>>>> +}
>>>>>>>> +
>>>>>>>> +static int qpnp_probe(struct spmi_device *sdev)
>>>>>>>> +{
>>>>>>>> +	struct device_node *root = sdev->dev.of_node;
>>>>>>>> +	struct device_node *child;
>>>>>>>> +	struct regmap *regmap;
>>>>>>>> +
>>>>>>>> +	regmap = devm_regmap_init_spmi_ext(sdev, &qpnp_regmap_config);
>>>>>>>> +	if (IS_ERR(regmap))
>>>>>>>> +		return PTR_ERR(regmap);
>>>>>>>> +
>>>>>>>> +	for_each_available_child_of_node(root, child)
>>>>>>>> +		qpnp_add_device(sdev, child);
>>>>>>>
>>>>>>> This entire driver looks like a re-write of of_platform_populate().
>>>>>>>
>>>>>>> Why?
>>>>>>
>>>>>> of_platform_populate is not used because the PMIC function resources are
>>>>>> non-translatable. You can see that the resources are of type
>>>>>> IORESOURCE_REG (qpnp_index_to_resource()) not IORESOURCE_MEM or _IO.
>>>>>>
>>>>>> The whole point of this mfd driver is to parse devicetree to prepare
>>>>>> resources for every child and create platform device for it through
>>>>>> mfd_add_devices(). Then the PMIC function driver got its resources and
>>>>>> use them as register addresses passed to regmap. These register accesses
>>>>>> hits the SPMI controller which is the physical interface between PMIC's
>>>>>> and SoC.
>>>>>
>>>>> I can't help but think that if this is required, it should be part of
>>>>> the core OF code, rather than doing your own thing which looks
>>>>> frighteningly like existing framework functionality.
>>>>
>>>> does it make sense to have a common of_mfd code for devicetree parsing?
>>>> Is that discussed already? I mean presently the mfd_cell resources and
>>>> number of resources are passed by the mfd_add_devices users. Is it
>>>> possible to have common code which parses devicetree sub-nodes of the
>>>> parent device_node and fill resources/create platform devices for them.
>>>
>>> I'm not sure it does.  Normally users _either_ represent devices in
>>> MFD cells from within the driver _or_ populate using existing DT
>>> interfaces i.e. of_platform_populate().  This is the first time I've
>>> seen someone attempt to parse the entire MFD node structure from
>>> within a driver.
>>
>> Our goal is to use common mfd driver for various Qualcomm PMIC from the
>> same PMIC generation (codenamed QPNP). Presently we have good
>> abstraction of the register manipulation functions through regmap-spmi
>> layer. Using the devicetree to represent different peripherals base
>> addresses (reg property) gives us a benefit by avoiding huge header
>> files in linux/mfd and make flexible transition to new PMIC's which just
>> change the base addresses but keep the IP block the same. This way we
>> should change the devicetree binding without touch the drivers.
> 
> I'm still not convinced that you need to write your own parser.  If
> you're concerned about not translating the reg property, use (or
> don't) the 'ranges' property accordingly.

Unfortunately "ranges" property doesn't help here. The pmic addresses
parsed from "reg" properties are SPMI addresses (similar to I2C addresses).

-- 
regards,
Stan
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