linux-kernel - Re: [PATCH 09/22] scsi: hisi_sas: retrieve SAS address for pci-based controller

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Date:   Thu, 18 May 2017 10:09:02 +0100
From:   John Garry <john.garry@...wei.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        John Garry <john.garry2@...l.dcu.ie>, <linuxarm@...wei.com>,
        <linux-scsi@...r.kernel.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 09/22] scsi: hisi_sas: retrieve SAS address for pci-based
 controller

>> Hi Arnd,
>>
>> Currently there is no pci device listed in the ACPI tables.
>>
>> What I am doing is declaring a fake device in the root of the System bus
>> tree of the ACPI tables, and in the kernel driver finding it by matching the
>> name. It is not the ACPI companion for the pci device.
>>
>> So I think that we can define the pci device under the pci bus in the ACPI
>> tables, and define the ADR and DSD. Then we would have an ACPI companion for
>> the device, and from that get the SAS address.
>
> Yes, that would be much better, and allow us to use the device properties
> interface directly. An additional advantage is that the property definition
> can be exactly the same as for the v1/v2 platform_device properties
> for anything that might be needed across all versions.  sas-addr already
> fits in there, and there might be additional properties you need in the
> future.
>

Hi Arnd,

OK, we'll try this.

As for other properties, phy and queue count are common to all versions.

However, I need to consider more if I should add these - maybe it is ok. 
The reason we did not hardcode these for v1/v2 was that these were 
variable for controllers inter and intra SoC.

hip08 only has 1 controller, and I have been told that each controller 
will have a unique pci device id that for future SoCs, so it's viable to 
hardcode.

>> An alternative to this ACPI device method is for UEFI to write the SAS
>> address to a defined free location in device's pci config space, which the
>> driver can read.
>
> That sounds ok as well, it would be nice to not rely on firmware data here,
> but I'd have to see how the implementation ends up: IIRC you should
> not just put the data at a fixed location in the config space but instead use
> the 'extended capabilities' infrastructure to find the data.
> PCI_EXT_CAP_ID_VNDR might be the right one here, but I don't
> know enough about this, so please consult with someone who does
> (or the PCIe specification).
>

Right, we'll keep ACPI table description as plan A.

>       Arnd
>

Much appreciated,
John

> .
>