linux-kernel - Re: [PATCH 2/6] mailbox: pcc: Wire up ->last_tx

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Message-ID: <88b406d0-919e-4357-8740-e87fce26e346@amperemail.onmicrosoft.com>
Date: Fri, 17 Oct 2025 12:59:11 -0400
From: Adam Young <admiyo@...eremail.onmicrosoft.com>
To: Sudeep Holla <sudeep.holla@....com>, linux-acpi@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: Adam Young <admiyo@...amperecomputing.com>,
 Robbie King <robbiek@...ghtlabs.com>, Huisong Li <lihuisong@...wei.com>,
 Jassi Brar <jassisinghbrar@...il.com>,
 Cristian Marussi <cristian.marussi@....com>
Subject: Re: [PATCH 2/6] mailbox: pcc: Wire up ->last_tx_done() for PCC
 channels

Correction.  I need to slow down.

Tested-by: Adam Young <admiyo@...amperecomputing.com>

On 10/17/25 12:48, Adam Young wrote:
> Tested-by: Adam Young <admiyo@...amperecompuing.com>
>
> On 10/16/25 15:08, Sudeep Holla wrote:
>> Some PCC users poll for completion between transfers and benefit from
>> the knowledge of previous Tx completion check through the mailbox
>> framework's ->last_tx_done() op.
>>
>> Hook up the last_tx_done callback in the PCC mailbox driver so the 
>> mailbox
>> framework can correctly query the completion status of the last 
>> transmitted
>> message. This aligns PCC with other controllers that already 
>> implement such
>> last_tx_done status query.
>>
>> No functional change unless callers use ->last_tx_done(). Normal Tx and
>> IRQ paths are unchanged. This change just improves synchronization and
>> avoids unnecessary timeouts for non-interrupt driven channels by 
>> ensuring
>> correct completion detection for PCC channels that don’t rely on 
>> interrupts.
>>
>> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
>> ---
>>   drivers/mailbox/pcc.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
>> index f6714c233f5a..2b690c268cf0 100644
>> --- a/drivers/mailbox/pcc.c
>> +++ b/drivers/mailbox/pcc.c
>> @@ -445,6 +445,13 @@ static int pcc_send_data(struct mbox_chan *chan, 
>> void *data)
>>       return ret;
>>   }
>>   +static bool pcc_last_tx_done(struct mbox_chan *chan)
>> +{
>> +    struct pcc_chan_info *pchan = chan->con_priv;
>> +
>> +    return pcc_mbox_cmd_complete_check(pchan);
>> +}
>> +
>>   /**
>>    * pcc_startup - Called from Mailbox Controller code. Used here
>>    *        to request the interrupt.
>> @@ -490,6 +497,7 @@ static const struct mbox_chan_ops pcc_chan_ops = {
>>       .send_data = pcc_send_data,
>>       .startup = pcc_startup,
>>       .shutdown = pcc_shutdown,
>> +    .last_tx_done = pcc_last_tx_done,
>>   };
>>     /**
>>