linux-kernel - Re: [PATCH 1/2] platform/x86: i2c-multi-instantiate: Add flag for passing fwnode

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Date:   Mon, 27 Apr 2020 14:51:23 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] platform/x86: i2c-multi-instantiate: Add flag for
 passing fwnode

Hi,

On 4/26/20 7:59 PM, Andy Shevchenko wrote:
> On Sun, Apr 26, 2020 at 1:47 PM Hans de Goede <hdegoede@...hat.com> wrote:
>>
>> In some cases the driver for the i2c_client-s which i2c-multi-instantiate
>> instantiates may need access some fields / methods from to the ACPI fwnode
>> for which i2c_clients are being instantiated.
>>
>> An example of this are CPLM3218 ACPI device-s. These contain CPM0 and
>> CPM1 packages with various information (e.g. register init values) which
>> the driver needs.
>>
>> Passing the fwnode through the i2c_board_info struct also gives the
>> i2c-core access to it, and if we do not pass an IRQ then the i2c-core
>> will use the fwnode to get an IRQ, see i2c_acpi_get_irq().
> 
> I'm wondering, can we rather do it in the same way like we do for
> GPIO/APIC case here.
> Introduce IRQ_RESOURCE_SHARED (or so) and
> 
> case _SHARED:
>   irq = i2c_acpi_get_irq();
> ...
> 
> ?

I think you are miss-understanding the problem. The problem is not that
we want to share the IRQ, the problem is that we want to pass the single
IRQ in the resources to only 1 of the instantiated I2C-clients. But if we
do not pass an IRQ (we leave it at 0) and we do pass the fwnode then
i2c-core-base.c will see that there is an ACPI-node attached to the
device and will call i2c_acpi_get_irq().

So the solution is definitely not calling i2c_acpi_get_irq() inside
i2c-multi-instantiate.c we want to avoid the i2c_acpi_get_irq(),
leaving the other 2 clients for the BSG1160 device without an IRQ
and thus avoiding the IRQ mismatch (it is a mismatch because the
drivers do not set the shared flag; and that is ok, we do not want
to share the IRQ, it is just for the accelerometer AFAIK).

Regards,

Hans


> 
>>
>> This is a problem when there is only an IRQ for 1 of the clients described
>> in the ACPI device we are instantiating clients for. If we unconditionally
>> pass the fwnode, then i2c_acpi_get_irq() will assign the same IRQ to all
>> clients instantiated, leading to kernel-oopses like this (BSG1160 device):
>>
>> [   27.340557] genirq: Flags mismatch irq 76. 00002001 (bmc150_magn_event) vs. 00000001 (bmc150_accel_event)
>> [   27.340567] Call Trace:
>> ...
>>
>> So we cannot simply always pass the fwnode. This commit adds a PASS_FWNODE
>> flag, which can be used to pass the fwnode in cases where we do not have
>> the IRQ problem and the driver for the instantiated client(s) needs access
>> to the fwnode.
>>
>> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
>> ---
>>   drivers/platform/x86/i2c-multi-instantiate.c | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/drivers/platform/x86/i2c-multi-instantiate.c b/drivers/platform/x86/i2c-multi-instantiate.c
>> index 6acc8457866e..dcafb1a29d17 100644
>> --- a/drivers/platform/x86/i2c-multi-instantiate.c
>> +++ b/drivers/platform/x86/i2c-multi-instantiate.c
>> @@ -20,6 +20,8 @@
>>   #define IRQ_RESOURCE_GPIO      1
>>   #define IRQ_RESOURCE_APIC      2
>>
>> +#define PASS_FWNODE            BIT(2)
>> +
>>   struct i2c_inst_data {
>>          const char *type;
>>          unsigned int flags;
>> @@ -93,6 +95,10 @@ static int i2c_multi_inst_probe(struct platform_device *pdev)
>>                  snprintf(name, sizeof(name), "%s-%s.%d", dev_name(dev),
>>                           inst_data[i].type, i);
>>                  board_info.dev_name = name;
>> +
>> +               if (inst_data[i].flags & PASS_FWNODE)
>> +                       board_info.fwnode = dev->fwnode;
>> +
>>                  switch (inst_data[i].flags & IRQ_RESOURCE_TYPE) {
>>                  case IRQ_RESOURCE_GPIO:
>>                          ret = acpi_dev_gpio_irq_get(adev, inst_data[i].irq_idx);
>> --
>> 2.26.0
>>
> 
>