Re: [PATCH 3/9] clk: sunxi: Add prcm mod0 clock driver

[Hans de Goede <hdegoede-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

Hi,

On 11/21/2014 09:49 AM, Maxime Ripard wrote:
> Hi,
> 
> On Thu, Nov 20, 2014 at 04:55:22PM +0100, Hans de Goede wrote:
>> Add a driver for mod0 clocks found in the prcm. Currently there is only
>> one mod0 clocks in the prcm, the ir clock.
>>
>> Signed-off-by: Hans de Goede <hdegoede-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
>> ---
>>  Documentation/devicetree/bindings/clock/sunxi.txt |  1 +
>>  drivers/clk/sunxi/Makefile                        |  2 +-
>>  drivers/clk/sunxi/clk-sun6i-prcm-mod0.c           | 63 +++++++++++++++++++++++
>>  drivers/mfd/sun6i-prcm.c                          | 14 +++++
>>  4 files changed, 79 insertions(+), 1 deletion(-)
>>  create mode 100644 drivers/clk/sunxi/clk-sun6i-prcm-mod0.c
>>
>> diff --git a/Documentation/devicetree/bindings/clock/sunxi.txt b/Documentation/devicetree/bindings/clock/sunxi.txt
>> index ed116df..342c75a 100644
>> --- a/Documentation/devicetree/bindings/clock/sunxi.txt
>> +++ b/Documentation/devicetree/bindings/clock/sunxi.txt
>> @@ -56,6 +56,7 @@ Required properties:
>>  	"allwinner,sun4i-a10-usb-clk" - for usb gates + resets on A10 / A20
>>  	"allwinner,sun5i-a13-usb-clk" - for usb gates + resets on A13
>>  	"allwinner,sun6i-a31-usb-clk" - for usb gates + resets on A31
>> +	"allwinner,sun6i-a31-ir-clk" - for the ir clock on A31
>>  
>>  Required properties for all clocks:
>>  - reg : shall be the control register address for the clock.
>> diff --git a/drivers/clk/sunxi/Makefile b/drivers/clk/sunxi/Makefile
>> index 7ddc2b5..daf8b1c 100644
>> --- a/drivers/clk/sunxi/Makefile
>> +++ b/drivers/clk/sunxi/Makefile
>> @@ -10,4 +10,4 @@ obj-y += clk-sun8i-mbus.o
>>  
>>  obj-$(CONFIG_MFD_SUN6I_PRCM) += \
>>  	clk-sun6i-ar100.o clk-sun6i-apb0.o clk-sun6i-apb0-gates.o \
>> -	clk-sun8i-apb0.o
>> +	clk-sun8i-apb0.o clk-sun6i-prcm-mod0.o
>> diff --git a/drivers/clk/sunxi/clk-sun6i-prcm-mod0.c b/drivers/clk/sunxi/clk-sun6i-prcm-mod0.c
>> new file mode 100644
>> index 0000000..e80f18e
>> --- /dev/null
>> +++ b/drivers/clk/sunxi/clk-sun6i-prcm-mod0.c
>> @@ -0,0 +1,63 @@
>> +/*
>> + * Allwinner A31 PRCM mod0 clock driver
>> + *
>> + * Copyright (C) 2014 Hans de Goede <hdegoede-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License as published by
>> + * the Free Software Foundation; either version 2 of the License, or
>> + * (at your option) any later version.
>> + *
>> + * 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/clk-provider.h>
>> +#include <linux/clkdev.h>
>> +#include <linux/module.h>
>> +#include <linux/of_address.h>
>> +#include <linux/platform_device.h>
>> +
>> +#include "clk-factors.h"
>> +#include "clk-mod0.h"
>> +
>> +static const struct of_device_id sun6i_a31_prcm_mod0_clk_dt_ids[] = {
>> +	{ .compatible = "allwinner,sun6i-a31-ir-clk" },
>> +	{ /* sentinel */ }
>> +};
>> +
>> +static DEFINE_SPINLOCK(sun6i_prcm_mod0_lock);
>> +
>> +static int sun6i_a31_prcm_mod0_clk_probe(struct platform_device *pdev)
>> +{
>> +	struct device_node *np = pdev->dev.of_node;
>> +	struct resource *r;
>> +	void __iomem *reg;
>> +
>> +	if (!np)
>> +		return -ENODEV;
>> +
>> +	r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>> +	reg = devm_ioremap_resource(&pdev->dev, r);
>> +	if (IS_ERR(reg))
>> +		return PTR_ERR(reg);
>> +
>> +	sunxi_factors_register(np, &sun4i_a10_mod0_data,
>> +			       &sun6i_prcm_mod0_lock, reg);
>> +	return 0;
>> +}
>> +
>> +static struct platform_driver sun6i_a31_prcm_mod0_clk_driver = {
>> +	.driver = {
>> +		.name = "sun6i-a31-prcm-mod0-clk",
>> +		.of_match_table = sun6i_a31_prcm_mod0_clk_dt_ids,
>> +	},
>> +	.probe = sun6i_a31_prcm_mod0_clk_probe,
>> +};
>> +module_platform_driver(sun6i_a31_prcm_mod0_clk_driver);
>> +
>> +MODULE_DESCRIPTION("Allwinner A31 PRCM mod0 clock driver");
>> +MODULE_AUTHOR("Hans de Goede <hdegoede-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>");
>> +MODULE_LICENSE("GPL");
> 
> I don't think this is the right approach, mainly for two reasons: the
> compatible shouldn't change, and you're basically duplicating code
> there.
> 
> I understand that you need the new compatible in order to avoid a
> double probing: one by CLK_OF_DECLARE, and one by the usual mechanism,
> and that also implies the second reason.

Not only for that, we need a new compatible also because the mfd framework
needs a separate compatible per sub-node as that is how it finds nodes
to attach to the platform devices, so we need a new compatible anyways,
with your make the mod0 clock driver a platform driver solution we could
use:

	compatible = "allwinner,sun6i-a31-ir-clk", "allwinner,sun4i-a10-mod0-clk";

To work around this, but there are other problems, your make mod0clk a
platform driver solution cannot work because the clocks node in the dtsi
is not simple-bus compatible, so no platform-devs will be instantiated for
the clocks there.

Besides the compatible (which as said we need a separate one anyways),
your other worry is code duplication, but I've avoided that as much
as possible already, the new drivers/clk/sunxi/clk-sun6i-prcm-mod0.c is
just a very thin wrapper, waying in with all of 63 lines including
16 lines GPL header.

So sorry, I disagree I believe that this is the best solution.

> However, as those are not critical clocks that need to be here early
> at boot, you can also fix this by turning the mod0 driver into a
> platform driver itself. The compatible will be kept, the driver will
> be the same.
> 
> The only thing we need to pay attention to is how "client" drivers
> react when they cannot grab their clock. They should return
> -EPROBE_DEFER, but that remains to be checked.

-EPROBE_DEFER is yet another reason to not make mod0-clk a platform
driver. Yes drivers should be able to handle this, but it is a pain,
and the more we use it the more pain it is. Also it makes booting a lot
slower as any driver using a mod0 clk now, will not complete its probe
until all the other drivers are done probing and the late_initcall
which starts the deferred-probe wq runs.

Regards,

Hans