linux-kernel - Re: [PATCH v4 3/6] libnvdimm, acpi, nfit: Add bus level dsm mask for pass thru.

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Date:   Sat, 1 Jul 2017 13:08:50 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Jerry Hoemann <Jerry.Hoemann@....com>
Cc:     "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 3/6] libnvdimm, acpi, nfit: Add bus level dsm mask for
 pass thru.

On Sat, Jul 1, 2017 at 12:58 PM, Jerry Hoemann <jerry.hoemann@....com> wrote:
> On Fri, Jun 30, 2017 at 08:55:22PM -0700, Dan Williams wrote:
>
> ...
>
>> On Fri, Jun 30, 2017 at 9:09 AM, Jerry Hoemann <jerry.hoemann@....com> wrote:
>> > +               if (cmd == ND_CMD_CALL)
>> > +                       dsm_mask = nd_desc->bus_dsm_mask;
>> >                 desc = nd_cmd_bus_desc(cmd);
>> >                 uuid = to_nfit_uuid(NFIT_DEV_BUS);
>> >                 handle = adev->handle;
>> > @@ -1613,6 +1615,7 @@ static void acpi_nfit_init_dsms(struct acpi_nfit_desc *acpi_desc)
>> >         struct nvdimm_bus_descriptor *nd_desc = &acpi_desc->nd_desc;
>> >         const u8 *uuid = to_nfit_uuid(NFIT_DEV_BUS);
>> >         struct acpi_device *adev;
>> > +       unsigned long dsm_mask;
>> >         int i;
>> >
>> >         nd_desc->cmd_mask = acpi_desc->bus_cmd_force_en;
>> > @@ -1624,6 +1627,11 @@ static void acpi_nfit_init_dsms(struct acpi_nfit_desc *acpi_desc)
>> >                 if (acpi_check_dsm(adev->handle, uuid, 1, 1ULL << i))
>> >                         set_bit(i, &nd_desc->cmd_mask);
>> >         set_bit(ND_CMD_CALL, &nd_desc->cmd_mask);
>> > +
>> > +       dsm_mask = 0x3bf;
>>
>> I went ahead and fixed this up to use dsm_mask defined like this:
>>
>> +       dsm_mask =
>> +               (1 << ND_CMD_ARS_CAP) |
>> +               (1 << ND_CMD_ARS_START) |
>> +               (1 << ND_CMD_ARS_STATUS) |
>> +               (1 << ND_CMD_CLEAR_ERROR) |
>> +               (1 << NFIT_CMD_TRANSLATE_SPA) |
>> +               (1 << NFIT_CMD_ARS_INJECT_SET) |
>> +               (1 << NFIT_CMD_ARS_INJECT_CLEAR) |
>> +               (1 << NFIT_CMD_ARS_INJECT_GET);
>>
>> This drops function number 0 which userspace has no need to call.
>
> Actually I like to call function 0.  Its an excellent test when
> modifying the code path as its a no side effects function whose output
> is known in advance and instantly recognizable.  I also use it when
> testing new firmware.
>
> What is the downside to allowing it?  What bad things happen?

It allows implementations to bypass the standardization process and
ship new root DSMs. It's always possible to patch the kernel locally
for development, so I see no reason to ship this capability globally.

> Also, I do have to ask why you allow function zero for NVDIMM_FAMILY_MSFT?

Yeah, that's an oversight / mistake, but it's also benign since it
can't be used to add support for new function numbers to the family
since all 32 numbers are already taken. We also allow override for
leaf devices since there's quite a bit more per vendor differentiation
that might take a while to standardize.