linux-kernel - Re: [PATCH v2 6/6] pci/hotplug/pnv_php: Enable third attention indicator

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Message-ID: <1469323476.1312174.1750293474949.JavaMail.zimbra@raptorengineeringinc.com>
Date: Wed, 18 Jun 2025 19:37:54 -0500 (CDT)
From: Timothy Pearson <tpearson@...torengineering.com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>, 
	linux-kernel <linux-kernel@...r.kernel.org>, 
	linux-pci <linux-pci@...r.kernel.org>, 
	Madhavan Srinivasan <maddy@...ux.ibm.com>, 
	Michael Ellerman <mpe@...erman.id.au>, 
	christophe leroy <christophe.leroy@...roup.eu>, 
	Naveen N Rao <naveen@...nel.org>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, 
	Shawn Anastasio <sanastasio@...torengineering.com>
Subject: Re: [PATCH v2 6/6] pci/hotplug/pnv_php: Enable third attention
 indicator



----- Original Message -----
> From: "Bjorn Helgaas" <helgaas@...nel.org>
> To: "Timothy Pearson" <tpearson@...torengineering.com>
> Cc: "linuxppc-dev" <linuxppc-dev@...ts.ozlabs.org>, "linux-kernel" <linux-kernel@...r.kernel.org>, "linux-pci"
> <linux-pci@...r.kernel.org>, "Madhavan Srinivasan" <maddy@...ux.ibm.com>, "Michael Ellerman" <mpe@...erman.id.au>,
> "christophe leroy" <christophe.leroy@...roup.eu>, "Naveen N Rao" <naveen@...nel.org>, "Bjorn Helgaas"
> <bhelgaas@...gle.com>, "Shawn Anastasio" <sanastasio@...torengineering.com>
> Sent: Wednesday, June 18, 2025 2:01:46 PM
> Subject: Re: [PATCH v2 6/6] pci/hotplug/pnv_php: Enable third attention indicator

> On Wed, Jun 18, 2025 at 11:58:59AM -0500, Timothy Pearson wrote:
>>  state
> 
> Weird wrapping of last word of subject to here.

I'll need to see what's up with my git format-patch setup. Apologies for that across the multiple series.

>> The PCIe specification allows three attention indicator states,
>> on, off, and blink.  Enable all three states instead of basic
>> on / off control.
>> 
>> Signed-off-by: Timothy Pearson <tpearson@...torengineering.com>
>> ---
>>  drivers/pci/hotplug/pnv_php.c | 15 ++++++++++++++-
>>  1 file changed, 14 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/pci/hotplug/pnv_php.c b/drivers/pci/hotplug/pnv_php.c
>> index 0ceb4a2c3c79..c3005324be3d 100644
>> --- a/drivers/pci/hotplug/pnv_php.c
>> +++ b/drivers/pci/hotplug/pnv_php.c
>> @@ -440,10 +440,23 @@ static int pnv_php_get_adapter_state(struct hotplug_slot
>> *slot, u8 *state)
>>  	return ret;
>>  }
>>  
>> +static int pnv_php_get_raw_indicator_status(struct hotplug_slot *slot, u8
>> *state)
>> +{
>> +	struct pnv_php_slot *php_slot = to_pnv_php_slot(slot);
>> +	struct pci_dev *bridge = php_slot->pdev;
>> +	u16 status;
>> +
>> +	pcie_capability_read_word(bridge, PCI_EXP_SLTCTL, &status);
>> +	*state = (status & (PCI_EXP_SLTCTL_AIC | PCI_EXP_SLTCTL_PIC)) >> 6;
> 
> Should be able to do this with FIELD_GET().

I used the same overall structure as the pciehp_hpc driver here.  Do you want me to also fix up that driver with FIELD_GET()?

> Is the PCI_EXP_SLTCTL_PIC part needed?  It wasn't there before, commit
> log doesn't mention it, and as far as I can tell, this would be the
> only driver to do that.  Most expose only the attention status (0=off,
> 1=on, 2=identify/blink).
> 
>> +	return 0;
>> +}
>> +
>> +
>>  static int pnv_php_get_attention_state(struct hotplug_slot *slot, u8 *state)
>>  {
>>  	struct pnv_php_slot *php_slot = to_pnv_php_slot(slot);
>>  
>> +	pnv_php_get_raw_indicator_status(slot, &php_slot->attention_state);
> 
> This is a change worth noting.  Previously we didn't read the AIC
> state from PCI_EXP_SLTCTL at all; we used php_slot->attention_state to
> keep track of whatever had been previously set via
> pnv_php_set_attention_state().
> 
> Now we read the current state from PCI_EXP_SLTCTL.  It's not clear
> that php_slot->attention_state is still needed at all.

It probably isn't.  It's unclear why IBM took this path at all, given pciehp's attention handlers predate pnv-php's by many years.

> Previously, the user could write any value at all to the sysfs
> "attention" file and then read that same value back.  After this
> patch, the user can still write anything, but reads will only return
> values with PCI_EXP_SLTCTL_AIC and PCI_EXP_SLTCTL_PIC.
> 
>>  	*state = php_slot->attention_state;
>>  	return 0;
>>  }
>> @@ -461,7 +474,7 @@ static int pnv_php_set_attention_state(struct hotplug_slot
>> *slot, u8 state)
>>  	mask = PCI_EXP_SLTCTL_AIC;
>>  
>>  	if (state)
>> -		new = PCI_EXP_SLTCTL_ATTN_IND_ON;
>> +		new = FIELD_PREP(PCI_EXP_SLTCTL_AIC, state);
> 
> This changes the behavior in some cases:
> 
>  write 0: previously turned indicator off, now writes reserved value
>  write 2: previously turned indicator on, now sets to blink
>  write 3: previously turned indicator on, now turns it off

If we're looking at normalizing with pciehp with an eye toward eventually deprecating / removing pnv-php, I can't think of a better time to change this behavior.  I suspect we're the only major user of this code path at the moment, with most software expecting to see pciehp-style handling.  Thoughts?