Re: [RFC] ARM: memory: da8xx-ddrctl: new driver

[Mark Rutland]

On Mon, Oct 24, 2016 at 06:46:36PM +0200, Bartosz Golaszewski wrote:
> Create a new driver for the da8xx DDR2/mDDR controller and implement
> support for writing to the Peripheral Bus Burst Priority Register.
> 
> Signed-off-by: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
> ---
>  .../memory-controllers/ti-da8xx-ddrctl.txt         |  20 +++
>  drivers/memory/Kconfig                             |   8 +
>  drivers/memory/Makefile                            |   1 +
>  drivers/memory/da8xx-ddrctl.c                      | 187 +++++++++++++++++++++
>  4 files changed, 216 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/memory-controllers/ti-da8xx-ddrctl.txt
>  create mode 100644 drivers/memory/da8xx-ddrctl.c
> 
> diff --git a/Documentation/devicetree/bindings/memory-controllers/ti-da8xx-ddrctl.txt b/Documentation/devicetree/bindings/memory-controllers/ti-da8xx-ddrctl.txt
> new file mode 100644
> index 0000000..f0eda59
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/memory-controllers/ti-da8xx-ddrctl.txt
> @@ -0,0 +1,20 @@
> +* Device tree bindings for Texas Instruments da8xx DDR2/mDDR memory controller
> +
> +The DDR2/mDDR memory controller present on Texas Instruments da8xx SoCs memory
> +maps a set of registers which allow to tweak the controller's behavior.

This is a description of the *driver*. The device itself doesn't map
some registers, it features them. Please descrive the *device*.

> +
> +Documentation:
> +OMAP-L138 (DA850) - http://www.ti.com/lit/ug/spruh82c/spruh82c.pdf
> +
> +Required properties:
> +
> +- compatible:		"ti,da850-ddrctl" - for da850 SoC based boards

Perhaps:

	"ti,da850-ddr-controller"

> +static int da8xx_ddrctl_probe(struct platform_device *pdev)
> +{
> +	const struct da8xx_ddrctl_config_knob *knob;
> +	const struct da8xx_ddrctl_setting *setting;
> +	u32 regprop[2], base, memsize, reg;
> +	struct device_node *node, *parent;
> +	void __iomem *ddrctl;
> +	const char *board;
> +	struct device *dev;
> +	int ret;
> +
> +	dev = &pdev->dev;
> +	node = dev->of_node;
> +
> +	/* Find the board name. */
> +	for (parent = node;
> +	     !of_node_is_root(parent);
> +	     parent = of_get_parent(parent));
> +
> +	ret = of_property_read_string(parent, "compatible", &board);
> +	if (ret) {
> +		dev_err(dev, "unable to read the soc model\n");
> +		return ret;
> +	}

I can see that you want to expose sysfs knobs for this, but is it really
necessary to match boards like this? It's very fragile, and commits us
to maintaining a database of board data (i.e. a board file).

I am very much not keen on that.

> +
> +	/* Check if we have settings for this board. */
> +	setting = da8xx_ddrctl_match_board(board);
> +	if (!setting) {
> +		dev_err(dev, "no settings for board '%s'\n", board);
> +		return -EINVAL;
> +	}

What's wrong with of_machine_is_compatible?

> +
> +	/* Figure out how to map the memory for the controller. */
> +	ret = of_property_read_u32_array(node, "reg", regprop, 2);
> +	if (ret) {
> +		dev_err(dev, "unable to parse 'reg' property\n");
> +		return ret;
> +	}
> +
> +	base = regprop[0];
> +	memsize = regprop[1];
> +
> +	ddrctl = ioremap(base, memsize);

NAK. Use the proper accessors for handling reg entries.

Thanks,
Mark.