Hi, On Fri, Feb 08, 2013 at 15:07:54, Mark Rutland wrote: > Hi, > > [...] > > > > > 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 > > [...] > > > > > > +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. > > > > > > + > > > > + 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. > > > > 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. > > 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 > > > > > > + 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. > > -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html