Hi,

On Fri, Feb 08, 2013 at 15:07:54, Mark Rutland wrote:

Hi,

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diff --git a/Documentation/devicetree/bindings/mmc/davinci_mmc.txt b/Documentation/devicetree/bindings/mmc/davinci_mmc.txt
new file mode 100644
index 0000000..6717ab1
--- /dev/null
+++ b/Documentation/devicetree/bindings/mmc/davinci_mmc.txt

@@ -0,0 +1,30 @@
+* TI Highspeed MMC host controller for DaVinci
+
+The Highspeed MMC Host Controller on TI DaVinci family
+provides an interface for MMC, SD and SDIO types of memory cards.
+
+This file documents the properties used by the davinci_mmc driver.
+
+Required properties:
+- compatible:
+ Should be "ti,davinci-mmc-da830": for da830, da850, dm365
+ Should be "ti,davinci-mmc-dm355": for dm355, dm644x
+
+Optional properties:
+- bus-width: Number of data lines, can be <4>, or <8>, default <1>
+- max-frequency: Maximum operating clock frequency, default 25MHz.
+- mmc-cap-mmc-highspeed: Indicates support for MMC in high speed mode
+- mmc-cap-sd-highspeed: Indicates support for SD in high speed mode

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+static struct davinci_mmc_config
+	*mmc_parse_pdata(struct platform_device *pdev)
 {
+	struct device_node *np;
 	struct davinci_mmc_config *pdata = pdev->dev.platform_data;
+	const struct of_device_id *match =
+		of_match_device(of_match_ptr(davinci_mmc_dt_ids), &pdev->dev);
+	u32 data;
+
+	np = pdev->dev.of_node;
+	if (!np)
+		return pdata;
+
+	pdata = devm_kzalloc(&pdev->dev, sizeof(*pdata), GFP_KERNEL);
+	if (!pdata) {
+		dev_err(&pdev->dev, "Failed to allocate memory for struct davinci_mmc_config\n");
+		goto nodata;
+	}
+
+	if (match->data)
+		pdata->version = (u8)((int)match->data);
+
+	of_property_read_u32(np, "max-frequency", &pdata->max_freq);
+	if (!pdata->max_freq)
+		dev_info(&pdev->dev, "'max-frequency' property not specified, defaulting to 25MHz\n");
+
+	if (of_get_property(np, "mmc-cap-mmc-highspeed", NULL))
+		pdata->caps |= MMC_CAP_MMC_HIGHSPEED;
+	if (of_get_property(np, "mmc-cap-sd-highspeed", NULL))
+		pdata->caps |= MMC_CAP_SD_HIGHSPEED;

If these aren't derivable from max-frequency, you could use
of_property_read_bool to make this clearer.

Correct, I will decide these based on max-frequency.

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+
+	of_property_read_u32(np, "bus-width", &data);
+	switch (data) {
+	case 0:

Judging by the binding doc, should this be 1 rather than 0?

By default driver comes up in 4 bit mode when bus-width is not specified.
Bus-width is set to 1 bit for invalid bus-widths. Below are the cases
when bus-width 0 or 4, bus-width is set to 4bit mode
When bus-width is 8, bus-width is set to 8 bit mode

Why is 0 a special value that means 4? Why not just use 4?

Here you just assign 0 to pdata->wires.

I see the current version of the driver handles this specially in
davinci_mmcsd_probe, but I don't see why this should leak into the binding.

Yes, I was trying to push in current driver behavior into binding documentation.

What I was originally trying to get at is that the binding says 8, 4, and 1 are
acceptable values, but you check the cases 8, 4, or 0. So you're accepting
something not documented, and producing a warning in a valid case (1).

Valid point.

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I thought that if somebody specifies bus-width as 2, 3, 5, 6, 7..., then
it should be defaulted to 1 bit mode, so I specified it as 1 bit in binding doc.

If they specify something invalid, falling back to a sane value with a warning
sounds good.

True.

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But I feel that a person who is editing dts file will not make such a mistake.
I will change binding document to default as 4 bit mode.

There have been and inevitably will be plenty of errors in dts files. I think
it'd be good to provide a warning and either use a value that's guaranteed to
work, or bail out if that can't be done.

If it's always valid to use 1 data line even if the hardware has more, I think
falling back to 1 makes more sense, as it'd be guaranteed to work.

I completely agree with you, thanks for your inputs.
Will add valid case 1:

Thanks,
Prakash

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+	case 4:
+	case 8:
+		pdata->wires = data;
+		break;
+	default:
+		pdata->wires = 1;
+		dev_info(&pdev->dev, "Unsupported buswidth, defaulting to 1 bit\n");
+	}
+nodata:
+	return pdata;
+}

With the first case changed to "case 1:", this block makes sense to me.

Thanks,
Mark.