Patchwork memory: add a basic OF-based memory driver

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Submitter Emilio López
Date Sept. 13, 2013, 12:30 a.m.
Message ID <1379032225-6425-1-git-send-email-emilio@elopez.com.ar>
Download mbox | patch
Permalink /patch/274623/
State New
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Comments

Emilio López - Sept. 13, 2013, 12:30 a.m.
This driver's only job is to claim and ensure the necessary clock
for memory operation on a DT-powered machine remains enabled.

Signed-off-by: Emilio López <emilio@elopez.com.ar>
---

I believe this new patch should resolve all the concerns raised; as
always, all feedback is welcome :)

Changes from RFC:
- Move from drivers/of to drivers/memory
- Make a proper driver instead of using an initcall
- Binding document for the new "simple-memory-controller"

 .../simple-memory-controller.txt                   | 19 ++++++++
 drivers/memory/Kconfig                             | 11 +++++
 drivers/memory/Makefile                            |  1 +
 drivers/memory/simple-mc.c                         | 57 ++++++++++++++++++++++
 4 files changed, 88 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/memory-controllers/simple-memory-controller.txt
 create mode 100644 drivers/memory/simple-mc.c
Olof Johansson - Sept. 13, 2013, 12:57 a.m.
On Thu, Sep 12, 2013 at 5:30 PM, Emilio López <emilio@elopez.com.ar> wrote:
> This driver's only job is to claim and ensure the necessary clock
> for memory operation on a DT-powered machine remains enabled.
>
> Signed-off-by: Emilio López <emilio@elopez.com.ar>
> ---
>
> I believe this new patch should resolve all the concerns raised; as
> always, all feedback is welcome :)

I think you're going about this the wrong way.

If you have a problem with a clock not staying on, shouldn't you just
marking it appropriately in the clock table instead, making sure it's
initialized with at least one reference to it? I believe that is how
some of the other platforms handle this, and it's a lot cleaner than
adding a fake binding and a fake driver just to grab a single clock.


-Olof
Emilio López - Sept. 13, 2013, 1:31 a.m.
Hi Olof,

El 12/09/13 21:57, Olof Johansson escribió:
> On Thu, Sep 12, 2013 at 5:30 PM, Emilio López <emilio@elopez.com.ar> wrote:
>> This driver's only job is to claim and ensure the necessary clock
>> for memory operation on a DT-powered machine remains enabled.
>>
>> Signed-off-by: Emilio López <emilio@elopez.com.ar>
>> ---
>>
>> I believe this new patch should resolve all the concerns raised; as
>> always, all feedback is welcome :)
>
> I think you're going about this the wrong way.
>
> If you have a problem with a clock not staying on, shouldn't you just
> marking it appropriately in the clock table instead, making sure it's
> initialized with at least one reference to it?

If by "the clock table" you mean the tree as handled by the common clock 
framework, there is no such flag available as of today; see Mike's reply 
for more information.

Personally I feel that if the general case can solve our problems (in 
this case, having a consumer who prepares and enables the clock), we 
should avoid adding special cases to the framework.

> I believe that is how
> some of the other platforms handle this, and it's a lot cleaner than
> adding a fake binding and a fake driver just to grab a single clock.

The binding doesn't have to be fake; it is actually describing the 
memory controller hardware:

mc: mc@0123000 {
	compatible = "simple-memory-controller";
	reg = <0x0123000 0x400>;
	clocks = <&pll5 1>;
};

If one day we get docs and/or have any special features we may need from 
the controller, we can use something like

mc: mc@0123000 {
	compatible = "vendor,awesome-mc", "simple-memory-controller";
	reg = <0x0123000 0x400>;
	clocks = <&pll5 1>;
};

Cheers,

Emilio
Rob Herring - Sept. 13, 2013, 2 p.m.
On Thu, Sep 12, 2013 at 8:31 PM, Emilio López <emilio@elopez.com.ar> wrote:
> Hi Olof,
>
> El 12/09/13 21:57, Olof Johansson escribió:
>
>> On Thu, Sep 12, 2013 at 5:30 PM, Emilio López <emilio@elopez.com.ar>
>> wrote:
>>>
>>> This driver's only job is to claim and ensure the necessary clock
>>> for memory operation on a DT-powered machine remains enabled.
>>>
>>> Signed-off-by: Emilio López <emilio@elopez.com.ar>
>>> ---
>>>
>>> I believe this new patch should resolve all the concerns raised; as
>>> always, all feedback is welcome :)
>>
>>
>> I think you're going about this the wrong way.
>>
>> If you have a problem with a clock not staying on, shouldn't you just
>> marking it appropriately in the clock table instead, making sure it's
>> initialized with at least one reference to it?
>
>
> If by "the clock table" you mean the tree as handled by the common clock
> framework, there is no such flag available as of today; see Mike's reply for
> more information.
>
> Personally I feel that if the general case can solve our problems (in this
> case, having a consumer who prepares and enables the clock), we should avoid
> adding special cases to the framework.
>
>
>> I believe that is how
>> some of the other platforms handle this, and it's a lot cleaner than
>> adding a fake binding and a fake driver just to grab a single clock.
>
>
> The binding doesn't have to be fake; it is actually describing the memory
> controller hardware:
>
> mc: mc@0123000 {
>         compatible = "simple-memory-controller";
>         reg = <0x0123000 0x400>;
>         clocks = <&pll5 1>;
> };
>
> If one day we get docs and/or have any special features we may need from the
> controller, we can use something like
>
> mc: mc@0123000 {
>         compatible = "vendor,awesome-mc", "simple-memory-controller";
>         reg = <0x0123000 0x400>;
>         clocks = <&pll5 1>;
> };

Better, but this is still wrong. DT describes the hardware. There is
no such h/w as a simple-memory-controller. The fact that you have a
simple-memory-ctrlr kernel driver is a kernel
feature/artifact/limitation. Describe the h/w with a meaningful
compatible string and put that string in the simple memory controller
driver match table. If someday we have a real driver for said memory
controller, then it is only a kernel change to use a different driver.

Rob
Olof Johansson - Sept. 13, 2013, 3:49 p.m.
On Fri, Sep 13, 2013 at 7:00 AM, Rob Herring <robherring2@gmail.com> wrote:
> On Thu, Sep 12, 2013 at 8:31 PM, Emilio López <emilio@elopez.com.ar> wrote:
>> Hi Olof,
>>
>> El 12/09/13 21:57, Olof Johansson escribió:
>>
>>> On Thu, Sep 12, 2013 at 5:30 PM, Emilio López <emilio@elopez.com.ar>
>>> wrote:
>>>>
>>>> This driver's only job is to claim and ensure the necessary clock
>>>> for memory operation on a DT-powered machine remains enabled.
>>>>
>>>> Signed-off-by: Emilio López <emilio@elopez.com.ar>
>>>> ---
>>>>
>>>> I believe this new patch should resolve all the concerns raised; as
>>>> always, all feedback is welcome :)
>>>
>>>
>>> I think you're going about this the wrong way.
>>>
>>> If you have a problem with a clock not staying on, shouldn't you just
>>> marking it appropriately in the clock table instead, making sure it's
>>> initialized with at least one reference to it?
>>
>>
>> If by "the clock table" you mean the tree as handled by the common clock
>> framework, there is no such flag available as of today; see Mike's reply for
>> more information.
>>
>> Personally I feel that if the general case can solve our problems (in this
>> case, having a consumer who prepares and enables the clock), we should avoid
>> adding special cases to the framework.
>>
>>
>>> I believe that is how
>>> some of the other platforms handle this, and it's a lot cleaner than
>>> adding a fake binding and a fake driver just to grab a single clock.
>>
>>
>> The binding doesn't have to be fake; it is actually describing the memory
>> controller hardware:
>>
>> mc: mc@0123000 {
>>         compatible = "simple-memory-controller";
>>         reg = <0x0123000 0x400>;
>>         clocks = <&pll5 1>;
>> };
>>
>> If one day we get docs and/or have any special features we may need from the
>> controller, we can use something like
>>
>> mc: mc@0123000 {
>>         compatible = "vendor,awesome-mc", "simple-memory-controller";
>>         reg = <0x0123000 0x400>;
>>         clocks = <&pll5 1>;
>> };
>
> Better, but this is still wrong. DT describes the hardware. There is
> no such h/w as a simple-memory-controller. The fact that you have a
> simple-memory-ctrlr kernel driver is a kernel
> feature/artifact/limitation. Describe the h/w with a meaningful
> compatible string and put that string in the simple memory controller
> driver match table. If someday we have a real driver for said memory
> controller, then it is only a kernel change to use a different driver.


We discussed this over IRC last night -- I still think it makes more
sense to make the clock driver for sunxi aware of this and just add a
reference to the clock at init time.

This is never going to differ from board to board (today the clock
name is the same on all sunxi platforms -- pll5_ddr. And the need will
likewise be there for all platforms at this time.

If and when it changes in the future, we can reevaluate. But this
doesn't have to be driven by device tree at this time, it seems to
just make things overly complicated and contrived.


-Olof
Rob Herring - Sept. 16, 2013, 12:55 p.m.
On Sun, Sep 15, 2013 at 7:43 AM, Grant Likely <grant.likely@linaro.org> wrote:
> On Fri, 13 Sep 2013 08:49:06 -0700, Olof Johansson <olof@lixom.net> wrote:
>> On Fri, Sep 13, 2013 at 7:00 AM, Rob Herring <robherring2@gmail.com> wrote:
>> > On Thu, Sep 12, 2013 at 8:31 PM, Emilio López <emilio@elopez.com.ar> wrote:

[snip]

>> > Better, but this is still wrong. DT describes the hardware. There is
>> > no such h/w as a simple-memory-controller. The fact that you have a
>> > simple-memory-ctrlr kernel driver is a kernel
>> > feature/artifact/limitation. Describe the h/w with a meaningful
>> > compatible string and put that string in the simple memory controller
>> > driver match table. If someday we have a real driver for said memory
>> > controller, then it is only a kernel change to use a different driver.
>>
>>
>> We discussed this over IRC last night -- I still think it makes more
>> sense to make the clock driver for sunxi aware of this and just add a
>> reference to the clock at init time.
>>
>> This is never going to differ from board to board (today the clock
>> name is the same on all sunxi platforms -- pll5_ddr. And the need will
>> likewise be there for all platforms at this time.
>>
>> If and when it changes in the future, we can reevaluate. But this
>> doesn't have to be driven by device tree at this time, it seems to
>> just make things overly complicated and contrived.
>
> I agree. Creating a new platform driver + device tree binding just to
> claim a clock that must not be disables does not look like the right
> approach to me either.

Maybe a driver is overkill, but fully describing the h/w would be a
good thing. Only defining the h/w that Linux currently uses is not a
good practice (although admittedly hard to avoid).

Rob

Patch

diff --git a/Documentation/devicetree/bindings/memory-controllers/simple-memory-controller.txt b/Documentation/devicetree/bindings/memory-controllers/simple-memory-controller.txt
new file mode 100644
index 0000000..d37683b
--- /dev/null
+++ b/Documentation/devicetree/bindings/memory-controllers/simple-memory-controller.txt
@@ -0,0 +1,19 @@ 
+Device Tree Clock binding for a simple memory controller.
+
+Required properties:
+- compatible : shall be "simple-memory-controller"
+
+Optional properties:
+- reg        : may contain the register space for the controller. This
+               property is currently ignored by the driver
+- clocks     : may contain a phandle to the clock that is currently being
+               used on the controller. This clock shall remain enabled
+               during system operation.
+
+Example:
+
+mc: mc@0123000 {
+	compatible = "simple-memory-controller";
+	reg = <0x0123000 0x400>;
+	clocks = <&pll5 1>;
+};
diff --git a/drivers/memory/Kconfig b/drivers/memory/Kconfig
index 29a11db..4a6df65 100644
--- a/drivers/memory/Kconfig
+++ b/drivers/memory/Kconfig
@@ -50,4 +50,15 @@  config TEGRA30_MC
 	  analysis, especially for IOMMU/SMMU(System Memory Management
 	  Unit) module.
 
+config SIMPLE_MC
+	bool "Simple memory controller"
+	default y
+	depends on OF && COMMON_CLK
+	help
+	  This driver is able to manage a simple memory controller whose
+	  only needs consist of keeping one clock enabled. The
+	  controller must be defined on the device tree as compatible
+	  with "simple-memory-controller"; see the corresponding binding
+	  document for more details.
+
 endif
diff --git a/drivers/memory/Makefile b/drivers/memory/Makefile
index 969d923..e0953e5 100644
--- a/drivers/memory/Makefile
+++ b/drivers/memory/Makefile
@@ -9,3 +9,4 @@  obj-$(CONFIG_TI_EMIF)		+= emif.o
 obj-$(CONFIG_MVEBU_DEVBUS)	+= mvebu-devbus.o
 obj-$(CONFIG_TEGRA20_MC)	+= tegra20-mc.o
 obj-$(CONFIG_TEGRA30_MC)	+= tegra30-mc.o
+obj-$(CONFIG_SIMPLE_MC)		+= simple-mc.o
diff --git a/drivers/memory/simple-mc.c b/drivers/memory/simple-mc.c
new file mode 100644
index 0000000..e58371d
--- /dev/null
+++ b/drivers/memory/simple-mc.c
@@ -0,0 +1,57 @@ 
+/*
+ * Simple memory controller driver
+ *
+ * Copyright 2013 Emilio López <emilio@elopez.com.ar>
+ *
+ * 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/of.h>
+#include <linux/clk.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+
+static int simple_mc_probe(struct platform_device *pdev)
+{
+	struct device_node *np = pdev->dev.of_node;
+	struct clk *clk;
+
+	if (!np)
+		return -ENODEV;
+
+	clk = of_clk_get(np, 0);
+	if (!IS_ERR(clk)) {
+		clk_prepare_enable(clk);
+		clk_put(clk);
+	}
+
+	return 0;
+}
+
+static const struct of_device_id simple_mc_of_match[] = {
+	{ .compatible = "simple-memory-controller", },
+	{ /* sentinel */ },
+};
+
+static struct platform_driver simple_mc_driver = {
+	.probe = simple_mc_probe,
+	.driver = {
+		.name = "simple-mc",
+		.owner = THIS_MODULE,
+		.of_match_table = of_match_ptr(simple_mc_of_match),
+	},
+};
+
+module_platform_driver(simple_mc_driver);
+
+MODULE_AUTHOR("Emilio López <emilio@elopez.com.ar>");
+MODULE_DESCRIPTION("Simple memory controller driver");
+MODULE_LICENSE("GPL");