Yes, it is unfortunate that different ACPI tables have different subtable headers, but that's the way it is. And, there are at least three different types, if not more. Bob > -----Original Message----- > From: Hanjun Guo [mailto:hanjun.guo@xxxxxxxxxx] > Sent: Saturday, May 02, 2015 7:02 AM > To: Timur Tabi; Zheng, Lv > Cc: Wysocki, Rafael J; Brown, Len; Lv Zheng; lkml; linux- > acpi@xxxxxxxxxxxxxxx; Tomasz Nowicki; Moore, Robert > Subject: Re: [PATCH 15/17] ACPICA/ARM: ACPI 5.1: Update for GTDT table > changes. > > Hi Timur, > > oh, you already noticed this issue, sorry for the noise in my previous > email. > > On 2015年05月02日 06:43, Timur Tabi wrote: > > On Tue, Jul 29, 2014 at 11:21 PM, Lv Zheng <lv.zheng@xxxxxxxxx> wrote: > >> From: Tomasz Nowicki <tomasz.nowicki@xxxxxxxxxx> > >> > >> New fields and new subtables. Tomasz Nowicki. > >> tomasz.nowicki@xxxxxxxxxx > >> > >> Signed-off-by: Tomasz Nowicki <tomasz.nowicki@xxxxxxxxxx> > >> Signed-off-by: Hanjun Guo <hanjun.guo@xxxxxxxxxx> > >> Signed-off-by: Bob Moore <robert.moore@xxxxxxxxx> > >> Signed-off-by: Lv Zheng <lv.zheng@xxxxxxxxx> > > > > 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? > > This is really a pain. I noticed this when I was prototyping the code for > GTDT in ACPI 5.1, and I even sent an email to Charles to ask him if there > are mistakes here, but there are chances that more than 255 bytes in that > structure so we must use u16 for the length. > > > > > 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. > > Yes, you can't use acpi_parse_entries() anymore, in my opinion, you can > introduce a similar function as acpi_parse_entries(), you can refer to > some code that parsing the structures with u16 length, the code I'm > familiar it's the code for Intel DMAR (similar with ARM IORT), for DMAR > table parsing, it has the same head as GTDT watchdog timer: > > /* DMAR subtable header */ > > struct acpi_dmar_header { > u16 type; > u16 length; > }; > > please refer to drivers/iommu/dmar.c and drivers/iommu/intel-iommu.c, hope > it helps. > > Thanks > Hanjun > > > > ��.n��������+%������w��{.n�����{�����ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f
