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Reply-To: minyard@acm.org
Subject: Re: [PATCH] ipmi:ssif: Fix double probe from tryacpi and trydmi
To:     Jiandi An <anjiandi@codeaurora.org>, arnd@arndb.de,
        gregkh@linuxfoundation.org
Cc:     openipmi-developer@lists.sourceforge.net,
        linux-kernel@vger.kernel.org
References: <1520401742-29371-1-git-send-email-anjiandi@codeaurora.org>
 <fa7367db-4199-3dd6-0e51-e991a5fd97fb@acm.org>
 <1bc40690-c46f-e7fd-1beb-37e362cd8146@codeaurora.org>
 <7814a839-a718-7437-3f69-8b4f090ccbcf@acm.org>
 <d3ff0287-56fa-de95-6de9-61c84d848b1c@codeaurora.org>
From:   Corey Minyard <minyard@acm.org>
Message-ID: <a462909d-4e1c-7dd8-8589-ac30d1730f83@acm.org>
Date:   Thu, 8 Mar 2018 14:40:51 -0600
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On 03/08/2018 12:18 PM, Jiandi An wrote:
>
>
> On 03/08/2018 08:10 AM, Corey Minyard wrote:
>> On 03/07/2018 05:59 PM, Jiandi An wrote:
>>>
>>>
>>> On 03/07/2018 07:34 AM, Corey Minyard wrote:
>>>> On 03/06/2018 11:49 PM, Jiandi An wrote:
>>>>> IPMI SSIF driver's parameter tryacpi and trydmi both
>>>>> are set to true.  The addition of IPMI DMI driver to
>>>>> create platform device for each IPMI device causes
>>>>> SSIF probe to be done twice on the same SMB I2C address
>>>>> for BMC.  Fix is to not call trydmi if tryacpi is able
>>>>> to find I2C address for BMC from SPMI ACPI table and
>>>>> probe successfully.
>>>>
>>>> Why are you trying to do this?  Is something bad happening?
>>>>
>>>> SPMI is not the preferred mechanism for detecting a device,
>>>> the preferred mechanism should be the acpi match table or
>>>> OF, followed by DMI, followed by SPMI.  In fact, it might be
>>>> best to just remove SPMI.
>>>>
>>>> -corey
>>>
>>>
>>> On our ARM64 platform, SSIF is the IPMI interface for host to
>>> BMC communication and it is described in ACPI SPMI table including
>>> the I2C address.  The driver would get the SSIF device from
>>> IPI0001 ssif_acpi_match[] and probe.  It worked fine with no issues.
>>>
>>> Then it was reported dmidecode does not show the correct SSIF
>>> device information including correct I2C address.  So SSIF device
>>> description is also added in SMBIOS table.  It worked fine with no
>>> issues until this patch.
>>>
>>> 0944d88 ipmi: Convert DMI handling over to a platform device
>>>
>>> We would see error message indicating trydmi via
>>> platform_driver_register fails with -EEXIST during boot.
>>>
>>> [    9.385758] ipmi_ssif: probe of dmi-ipmi-ssif.0 failed with error 
>>> -17
>>>
>>> This is because tryacpi ran first and successfully completed
>>> new_ssif_client() (which adds address to ssif_info) and eventually
>>> ssif_probe()
>>>
>>> ssif_tryacpi
>>>     spmi_find_bmc()
>>>         try_init_spmi()
>>>             new_ssif_client()
>>>
>>> Since both tryacpi and trydmi are set to true as module parameter
>>> with no permission and not exposed to /sys/module/ipmi_ssif/parameters,
>>> it triggers the following path down to dmi_ipmi_probe() and
>>> new_ssif_client() which fails ssif_info_find() finds the address
>>> added to ssif_info already in the ssif_tryacpi path.
>>>
>>> ssif_trydmi
>>>     platform_driver_register(&ipmi_driver)
>>>         __platform_driver_register()
>>>             driver_register()
>>>                 bus_add_driver()
>>>                     driver_attach()
>>>                         bus_for_each_dev()
>>>                             __driver_attach()
>>>                                 driver_probe_device()
>>>                                     ssif_platform_probe()
>>>                                         dmi_ipmi_probe()
>>>                                             new_ssif_client()
>>>
>>> Are you suggesting to not do tryacpi at all and just rely on
>>> trydmi?
>>
>> Basically, yes.  SPMI is really designed for early detection of 
>> interfaces
>> before ACPI proper comes up.  You should have the IPMI device in your
>> ACPI tree.
>
> You meant to say I should have the IPMI SSIF device in my SMBIOS table?
> Or do you mean to say I should have the IPMI SSIF device in my ACPI SPMI
> table but you will remove SPMI support from the IPMI driver?

I mean that you should have the IPMI SSIF device in your ACPI namespace
(see section C3-2 in the IPMI spec) and that should be the preferred
method for locating the system interfaces.  If it doesn't get detected by
that interface, then any ACPI methods that require IPMI will not work.
SMBIOS detection should be secondary.  SPMI really shouldn't be used.

This is something I have been meaning to work on for a while, let me
work on this a bit and I'll send you some patches.

-corey

>
> Do you want me to remove the ssif_tryacpi logic and tryacpi module
> parameter all together in that patch?
>
> Thanks
> -Jiandi
>
>>
>> My inclination is to remove SPMI support from the IPMI driver.
>>
>> -corey
>> >>
>>> I was looking at the following patch to understand more about
>>> the added ipmi_dmi driver.
>>>
>>> 9f88145 ipmi: Create a platform device for a DMI-specified IPMI 
>>> interface
>>>
>>> It's creating a platform device for each IPMI device in the DMI
>>> table including SSIF device, for auto-loading IPMI devices from
>>> SMBIOS tables.
>>>
>>> Are you suggesting removing SSIF device description from ACPI
>>> SPMI table and remove ssif_tryacpi logic all together?
>>>
>>> But the commit description mentions ...
>>>
>>> "This also adds the ability to extract the slave address from
>>> the SMBIOS tables, so that when the driver uses ACPI-specified
>>> interfaces, it can still extract the slave address from SMBIOS."
>>>
>>> This made me think SSIF driver can still use ACPI-specified
>>> interface.  It made me think it implies SSIF device can be
>>> described in ACPI SPMI table and SMBIOS table.  Both spec
>>> did not say they cannot.
>>>
>>> What's your recommended way of fixing this double probing?
>>>
>>> Thanks
>>>
>>>
>>>>
>>>>> Signed-off-by: Jiandi An <anjiandi@codeaurora.org>
>>>>> ---
>>>>>   drivers/char/ipmi/ipmi_ssif.c | 35 
>>>>> ++++++++++++++++++++++++-----------
>>>>>   1 file changed, 24 insertions(+), 11 deletions(-)
>>>>>
>>>>> diff --git a/drivers/char/ipmi/ipmi_ssif.c 
>>>>> b/drivers/char/ipmi/ipmi_ssif.c
>>>>> index 9d3b0fa..5c57363 100644
>>>>> --- a/drivers/char/ipmi/ipmi_ssif.c
>>>>> +++ b/drivers/char/ipmi/ipmi_ssif.c
>>>>> @@ -1981,29 +1981,41 @@ static int try_init_spmi(struct SPMITable 
>>>>> *spmi)
>>>>>       return new_ssif_client(myaddr, NULL, 0, 0, SI_SPMI, NULL);
>>>>>   }
>>>>> -static void spmi_find_bmc(void)
>>>>> +static int spmi_find_bmc(void)
>>>>>   {
>>>>>       acpi_status      status;
>>>>>       struct SPMITable *spmi;
>>>>>       int              i;
>>>>> +    int              rc = 0;
>>>>>       if (acpi_disabled)
>>>>> -        return;
>>>>> +        return -EPERM;
>>>>>       if (acpi_failure)
>>>>> -        return;
>>>>> +        return -ENODEV;
>>>>>       for (i = 0; ; i++) {
>>>>>           status = acpi_get_table(ACPI_SIG_SPMI, i+1,
>>>>>                       (struct acpi_table_header **)&spmi);
>>>>> -        if (status != AE_OK)
>>>>> -            return;
>>>>> +        if (status != AE_OK) {
>>>>> +            if (i == 0)
>>>>> +                return -ENODEV;
>>>>> +            else
>>>>> +                return 0;
>>>>> +        }
>>>>> -        try_init_spmi(spmi);
>>>>> +        rc = try_init_spmi(spmi);
>>>>> +        if (rc)
>>>>> +            return rc;
>>>>>       }
>>>>> +
>>>>> +    return 0;
>>>>>   }
>>>>>   #else
>>>>> -static void spmi_find_bmc(void) { }
>>>>> +static int spmi_find_bmc(void)
>>>>> +{
>>>>> +    return -ENODEV;
>>>>> +}
>>>>>   #endif
>>>>>   #ifdef CONFIG_DMI
>>>>> @@ -2104,12 +2116,13 @@ static int init_ipmi_ssif(void)
>>>>>                      addr[i]);
>>>>>       }
>>>>> -    if (ssif_tryacpi)
>>>>> +    if (ssif_tryacpi) {
>>>>>           ssif_i2c_driver.driver.acpi_match_table    =
>>>>>               ACPI_PTR(ssif_acpi_match);
>>>>> -
>>>>> -    if (ssif_tryacpi)
>>>>> -        spmi_find_bmc();
>>>>> +        rv = spmi_find_bmc();
>>>>> +        if (!rv)
>>>>> +            ssif_trydmi = false;
>>>>> +    }
>>>>>       if (ssif_trydmi) {
>>>>>           rv = platform_driver_register(&ipmi_driver);
>>>>
>>>>
>>>
>>
>