linux-kernel - Re: [PATCH 0/1] Compact interface for Device-Tree

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Date:	Sat, 1 Nov 2014 05:13:45 +0800
From:	Rob Herring <robherring2@...il.com>
To:	Gilad Avidov <gavidov@...eaurora.org>
Cc:	Rob Herring <robh+dt@...nel.org>, Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Grant Likely <grant.likely@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Sagar Dharia <sdharia@...eaurora.org>,
	linux-arm-msm <linux-arm-msm@...r.kernel.org>,
	David Woodhouse <dwmw2@...radead.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 0/1] Compact interface for Device-Tree

On Fri, Oct 31, 2014 at 6:59 AM, Gilad Avidov <gavidov@...eaurora.org> wrote:
>
> Device-Tree compact API
> ------------------------
>
> Common code seen in driver’s probe reads device tree values and handling
> erroneous return codes from all those of_property_read_xxx()  APIs. This
> common code is factored out by the of_property_map module which allows
> driver’s probe to replace that (often lengthy) code with a concise table:
>
> struct of_prop_map map[] = {
>     {"i2c",            &dev->id,        OF_REQ,  OF_ID,  -1},
>     {"qcom,clk-freq-out",    &dev->clk_freq_out,    OF_REQ,  OF_U32,  0},
>     {"qcom,clk-freq-in",    &dev->clk_freq_in,    OF_REQ,  OF_U32,  0},
>     {"qcom,disable-dma",    &dev->disable_dma,    OF_OPT,  OF_BOOL, 0},
>     {"qcom,master-id",    &dev->mstr_id,        OF_SGST, OF_U32,  0},
>     {NULL,            NULL,            0,       0,       0},
> };
>
> Then call populate to read the values into the device’s variables:
>
> ret = of_prop_populate(dev, dev->of_node, map);

Interesting idea. The main concern I have with this is there has been
on-going discussions about how to generalize property handling across
DT and ACPI to make drivers more agnostic, so I'm copying a few folks
involved in that. That may be a bit orthogonal to what this is doing,
but we may want some coordination here.

BTW, there is little point to a 0/1 email. All this info should be in
the patch either in commit msg or documentation as part of the patch.

Rob

> An equivalent code snippet using the traditional of_property_read_XXXX()
> API. Note that the equivalent is longer and more difficult to follow and
> debug:
>
> /* optional property */
> dev->disable_dma = of_property_read_bool(node, "qcom,disable-dma");
>
> ret = of_property_read_u32(dev->node, "qcom,clk-freq-out", &dev->clk_freq_out);
> if (ret) {
>     dev_err(dev, "error: missing 'qcom,clk-freq-out' DT property\n");
>     if (!err)
>         err = ret;
> }
>
> ret = of_property_read_u32(dev->node, "qcom,clk-freq-in", &dev->clk_freq_in);
> if (ret) {
>     dev_err(dev, "error: missing 'qcom,clk-freq-in' DT property\n");
>     if (!err)
>         err = ret;
> }
>
> /* suggested property */
> ret = of_property_read_u32(dev->node, "qcom,master-id", &dev->mstr_id);
> if (ret && !err)
>     err = ret;
>
>
> ret = of_alias_get_id(dev->node, "i2c");
> if (ret < 0) {
>     dev_err(dev, "error: missing '"i2c"' DT property\n");
>     if (!err)
>         err = ret;
> } else {
>     dev->id = ret;
> }
>
>
> The Device-Tree node and alias which are read by the above code snippets:
>
> aliases {
>     i2c0 = &i2c_0; /* I2C0 controller device */
> };
>
> i2c_0: i2c@...6000 { /* BLSP1 QUP2 */
>     compatible = "qcom,i2c-msm-v2";
>     reg-names = "qup_phys_addr", "bam_phys_addr";
>     reg = <0x78b6000 0x600>,
>           <0x7884000 0x23000>;
>     qcom,clk-freq-out = <100000>;
>     qcom,clk-freq-in  = <19200000>;
>     qcom,disable-dma;
>     qcom,master-id = <86>;
> };
>
>
> Gilad Avidov (1):
>   of_propery_map: compact interface for Device-Tree
>
>  Documentation/devicetree/of_property_map.txt |   76 ++++++++++++++++++++++
>  drivers/of/Makefile                          |    2 +-
>  drivers/of/of_property_map.c                 |   88 ++++++++++++++++++++++++++
>  include/linux/of_property_map.h              |   74 ++++++++++++++++++++++
>  4 files changed, 239 insertions(+), 1 deletion(-)
>  create mode 100644 Documentation/devicetree/of_property_map.txt
>  create mode 100644 drivers/of/of_property_map.c
>  create mode 100644 include/linux/of_property_map.h
>
> --
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> hosted by The Linux Foundation
>
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