linux-kernel - Re: [PATCH 15/17] ACPICA/ARM: ACPI 5.1: Update for GTDT table changes.

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Date:	Fri, 1 May 2015 17:43:39 -0500
From:	Timur Tabi <timur@...eaurora.org>
To:	Lv Zheng <lv.zheng@...el.com>
Cc:	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Len Brown <len.brown@...el.com>, Lv Zheng <zetalog@...il.com>,
	lkml <linux-kernel@...r.kernel.org>, linux-acpi@...r.kernel.org,
	Tomasz Nowicki <tomasz.nowicki@...aro.org>,
	Hanjun Guo <hanjun.guo@...aro.org>,
	Bob Moore <robert.moore@...el.com>
Subject: Re: [PATCH 15/17] ACPICA/ARM: ACPI 5.1: Update for GTDT table changes.

On Tue, Jul 29, 2014 at 11:21 PM, Lv Zheng <lv.zheng@...el.com> wrote:
> From: Tomasz Nowicki <tomasz.nowicki@...aro.org>
>
> New fields and new subtables. Tomasz Nowicki.
> tomasz.nowicki@...aro.org
>
> Signed-off-by: Tomasz Nowicki <tomasz.nowicki@...aro.org>
> Signed-off-by: Hanjun Guo <hanjun.guo@...aro.org>
> Signed-off-by: Bob Moore <robert.moore@...el.com>
> Signed-off-by: Lv Zheng <lv.zheng@...el.com>

Hi, I know this patch is old, but something confuses me about it:

> +/* Common GTDT subtable header */
> +
> +struct acpi_gtdt_header {
> +       u8 type;
> +       u16 length;
> +};

I'm trying to write a function that parses the watchdog structure
(acpi_gtdt_watchdog).  The first entry in that structure is
acpi_gtdt_header.  Looking at the ACPI specification, I see that this
is correct: the type is one byte, and the length is two bytes.

However, this means that I cannot use acpi_parse_entries() to parse
the watchdog subtable:

int __init
acpi_parse_entries(char *id, unsigned long table_size,
        acpi_tbl_entry_handler handler,
        struct acpi_table_header *table_header,
        int entry_id, unsigned int max_entries)

acpi_tbl_entry_handler takes an acpi_subtable_header as its first
parameter.  However, that structure looks like this:

struct acpi_subtable_header {
    u8 type;
    u8 length;
};

This is not compatible, so I'm confused now.  How do I properly parse
the watchdog subtable, if I cannot use acpi_parse_entries?

For context, here is my patch:

http://www.spinics.net/lists/linux-watchdog/msg06240.html

Scroll down to function arm_sbsa_wdt_parse_gtdt().  The typecast in
first line is invalid:

+    struct acpi_gtdt_watchdog *wdg = (struct acpi_gtdt_watchdog *)header;

because of the mismatch.  I don't know how to fix this.
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