Re: [PATCH V5 07/15] pci, acpi: Provide generic way to assign bus domain number.

[Tomasz Nowicki]

On 17.02.2016 16:21, Jayachandran Chandrashekaran Nair wrote:
> On Wed, Feb 17, 2016 at 8:35 PM, Tomasz Nowicki <tn@xxxxxxxxxxxx> wrote:
> > On 17.02.2016 15:21, Jayachandran Chandrashekaran Nair wrote:
> > > On Wed, Feb 17, 2016 at 7:37 PM, Tomasz Nowicki <tn@xxxxxxxxxxxx> wrote:
> > > > On 17.02.2016 14:44, Jayachandran Chandrashekaran Nair wrote:
> > > > > Tomasz, Lorenzo,
> > > > >
> > > > > On Tue, Feb 16, 2016 at 7:23 PM, Tomasz Nowicki<tn@xxxxxxxxxxxx>  wrote:
> > > > > > > As we now have valid PCI host bridge device reference we can
> > > > > > > introduce code that is going to find its bus domain number using
> > > > > > > ACPI _SEG method.
> > > > > > >
> > > > > > > Note that _SEG method is optional, therefore _SEG absence means
> > > > > > > that all PCI buses belong to domain 0.
> > > > > > >
> > > > > > > While at it, for the sake of code clarity we put ACPI and DT domain
> > > > > > > assign methods into the corresponding helpers.
> > > > >
> > > > >
> > > > > In my patchset, I had a slightly different and I think better approach
> > > > > for
> > > > > this without calling the _SEG method again. Please see
> > > > > http://www.spinics.net/lists/arm-kernel/msg478167.html
> > > > > at the last part
> > > > > ofhttp://www.spinics.net/lists/arm-kernel/msg478169.html
> > > >
> > > >
> > > > Relying on NULL parent device to make decision on boot method is really
> > > > ugly
> > > > way. This may hit us again once we want to obtain another firmware
> > > > specific
> > > > info e.g. numa node. IMO we need to fix it this way.
> > >
> > >
> > > I am not relying on NULL there, in the current code parent is NULL
> > > in case of ACPI, and the check is needed not to crash (unless that
> > > has changed).
> >
> >
> > This series passes down valid parent, see [PATCH V5 06/15].
> >
> > > The main part was the macro acpi_pci_get_segment() and the use
> > > of acpi_pci_root_info from sysdata to do this.
> >
> >
> > Since we can obtain related firmware specific data from valid parent device
> > (without defining another accessors), I do not see the point to use sysdata.
> > Let me know your opinion.
>
> In the patch, you use the parent info and call _SEG method again.
> The segment information is available in the ->root->segment of
> acpi_pci_root_info if you setup the sysdata like in my patch

I know it is in sysdata->root->segment, but the way it is passed down is 
wrong. sysdata is the pointer to unknown content (void *) so we need to 
validate it before we can use it. If we merge this patch we can remove 
first _SEG call.

Tomasz