RE: [PATCH] ACPI/IORT: fix the iort_id_map function

Pankaj Bansal <pankaj.bansal@xxxxxxx> · Mon, 16 Dec 2019 05:14:40 +0000

Hi Hanjun,

Thanks for replying. Please find my response inline

> -----Original Message-----
> From: Hanjun Guo <guohanjun@xxxxxxxxxx>
> Sent: Monday, 16 December, 2019 09:19 AM
> To: Pankaj Bansal <pankaj.bansal@xxxxxxx>; Lorenzo Pieralisi
> <lorenzo.pieralisi@xxxxxxx>; Sudeep Holla <sudeep.holla@xxxxxxx>;
> Rafael J . Wysocki <rjw@xxxxxxxxxxxxx>; Len Brown <lenb@xxxxxxxxxx>
> Cc: linux-acpi@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>
> Subject: Re: [PATCH] ACPI/IORT: fix the iort_id_map function
> 
> Hi Pankaj,
> 
> On 2019/12/15 23:12, Pankaj Bansal wrote:
> > As per
> > https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Finfoc
> >
> enter.arm.com%2Fhelp%2Ftopic%2Fcom.arm.doc.den0049d%2FDEN0049D_IO
> _Rema
> >
> pping_Table.pdf&amp;data=02%7C01%7Cpankaj.bansal%40nxp.com%7C78d
> 82a560
> >
> 5714219196008d781db06a7%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%
> 7C1%7C6
> >
> 37120650018983814&amp;sdata=%2FRhATUKx%2FA2gPEx%2BNY9X%2F7kqV
> CrEeRnbE%
> > 2B2qlTkdGDc%3D&amp;reserved=0
> > in ID mappings:
> > Number of IDs = The number of IDs in the range minus one.
> 
> Hmm, the spec is confusing, the spec may need to be updated, for example,
> for a PCI bus, device ID + function ID will take 8 bits and will be 256 IDs for
> that PCI bus, not sure why we need to minus one.
> 

I agree that this "minus one" thing is confusing. Not sure why It was put in the spec
like that. I guess they wanted the number of IDs to be 0 based instead of 1 based.

> >
> > Therefore, it's valid for ID mapping to contain single device mapping
> > which would have Number of IDs field 0.
> 
> Why not use single mapping flag for this case?

Actually single mapping flag doesn't mean that there is single mapping in an ID mapping.
It means that Input ID should not be considered when looking for Output ID.
If we put single id flag, then we cannot have a case where we have an array of single mappings
for one device.
e.g. an array of single mappings for one PCIe Root Complex, where we have a unique output ID for a unique BDF(Input ID)

> 
> Thanks
> Hanjun

Regards,
Pankaj Bansal