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SubjectRe: [PATCH RFC 2/2] soc: Add a basic ACPI generic driver
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On 28/01/2020 12:50, Arnd Bergmann wrote:

Hi Arnd,

> On Tue, Jan 28, 2020 at 12:18 PM John Garry <john.garry@huawei.com> wrote:
>>
>> Add a generic driver for platforms which populate their ACPI PPTT
>> processor package ID Type Structure according to suggestion in the ACPI
>> spec - see ACPI 6.2, section 5.2.29.3 ID structure Type 2.
>>
>> The soc_id is from member LEVEL_2_ID.
>>
>> For this, we need to use a whitelist of platforms which are known to
>> populate the structure as suggested.
>>
>> For now, only the vendor and soc_id fields are exposed.
>>
>> Signed-off-by: John Garry <john.garry@huawei.com>
>
> Would it be possible to make this the root device for all on-chip devices
> to correctly reflect the hierarchy inside of the soc?

I don't think so. The information about the SoC is got from the PPTT,
which only describes processors, caches, and physical package
boundaries. It doesn't include references to on-chip devices.

Having said that (and unrelated to this series), we could add
/sys/devices/system/soc folder, similar to node folder.

>
>> +/*
>> + * Known platforms that fill in PPTT package ID structures according to
>> + * ACPI spec examples, that being:
>> + * - Custom driver attribute is in ID Type Structure VENDOR_ID member
>> + * - SoC id is in ID Type Structure LEVEL_2_ID member
>> + * See ACPI SPEC 6.2 Table 5-154 for PPTT ID Type Structure
>> + */
>> +static struct acpi_platform_list plat_list[] = {
>> + {"HISI ", "HIP08 ", 0, ACPI_SIG_PPTT, all_versions},
>> + { } /* End */
>> +};
>
> That matches a single machine, right? It doesn't seem very generic
> that way.

Yes :) The problem is that the PPTT ID structure is open to use how the
implementer wants, so we can't assume everything/anything implemented
according to the spec examples. Maybe we could call it type1 or
something like that for platforms which did use the convention in the
spec example.

>
>> +struct acpi_generic_soc_struct {
>> + struct soc_device_attribute dev_attr;
>> + u32 vendor;
>> +};
>> +
>> +static ssize_t vendor_show(struct device *dev,
>> + struct device_attribute *attr,
>> + char *buf)
>> +{
>> + struct acpi_generic_soc_struct *soc = dev_get_drvdata(dev);
>> + u8 vendor_id[5] = {};
>> +
>> + *(u32 *)vendor_id = soc->vendor;
>> +
>> + return sprintf(buf, "%s\n", vendor_id);
>> +}
>
> I'd rather not see nonstandard attributes in a "generic" driver at
> all. Maybe the
> you can simply concatenate the vendor and LEVEL_2_ID into a single string
> here?

I actually don't really require the vendor attr. And since "vendor" is
not in the set of standard soc driver attrs, it can just be omitted.

>
>> + soc = kzalloc(sizeof(*soc), GFP_KERNEL);
>> + if (!soc)
>> + return -ENOMEM;
>> +
>> + soc_dev_attr = &soc->dev_attr;
>> + soc_dev_attr->soc_id = kasprintf(GFP_KERNEL, "%s",
>> + soc_id);
>
> On the other hand, it would make sense to fill out additional fields here.
> You have already matched the name of the board from the
> acpi_platform_list, so there are two strings available that could be put
> into the "machine" field, and it would make sense to fill out "family" with
> something that identifies it as coming from ACPI PPTT data.

OK, maybe the ones you suggested could be added. I did just want to
start out with a minimal sets of files, especially since we don't always
have a direct mapping between soc driver attrs and this PPTT ID structure.

Thanks,
John

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