linux-kernel - Re: [PATCH 1/2] mailbox: reset txdone_method TXDONE_BY_POLL if client knows

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Date:   Mon, 3 Jul 2017 13:55:29 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Jassi Brar <jaswinder.singh@...aro.org>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Jassi Brar <jassisinghbrar@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Alexey Klimov <alexey.klimov@....com>
Subject: Re: [PATCH 1/2] mailbox: reset txdone_method TXDONE_BY_POLL if client
 knows_txdone



On 03/07/17 12:50, Jassi Brar wrote:
> On 3 July 2017 at 15:05, Sudeep Holla <sudeep.holla@....com> wrote:
>>
>>
>> On 03/07/17 09:57, Sudeep Holla wrote:
>>>
>>>
>>> On 01/07/17 12:25, Jassi Brar wrote:
>>>> On Fri, Jun 30, 2017 at 8:44 PM, Sudeep Holla <sudeep.holla@....com> wrote:
>>>>> Currently the mailbox framework sets txdone_method to TXDONE_BY_POLL if
>>>>> the controller sets txdone_by_poll. However some clients can have a
>>>>> mechanism to do TXDONE_BY_ACK which they can specify by knows_txdone.
>>>>> However, we endup setting both TXDONE_BY_POLL and TXDONE_BY_ACK in that
>>>>> case. In such scenario, we may end up with below warnings as the tx
>>>>> ticker is run both by mailbox framework and the client.
>>>>>
>>>>> WARNING: CPU: 1 PID: 0 at kernel/time/hrtimer.c:805 hrtimer_forward+0x88/0xd8
>>>>> CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.12.0-rc5 #242
>>>>> Hardware name: ARM LTD ARM Juno Development Platform
>>>>> task: ffff8009768ca700 task.stack: ffff8009768f8000
>>>>> PC is at hrtimer_forward+0x88/0xd8
>>>>> LR is at txdone_hrtimer+0xd4/0xf8
>>>>> Call trace:
>>>>>  hrtimer_forward+0x88/0xd8
>>>>>  __hrtimer_run_queues+0xe4/0x158
>>>>>  hrtimer_interrupt+0xa4/0x220
>>>>>  arch_timer_handler_phys+0x30/0x40
>>>>>  handle_percpu_devid_irq+0x78/0x130
>>>>>  generic_handle_irq+0x24/0x38
>>>>>  __handle_domain_irq+0x5c/0xb8
>>>>>  gic_handle_irq+0x54/0xa8
>>>>>
>>>>> This patch fixes the issue by resetting TXDONE_BY_POLL if client has set
>>>>> knows_txdone.
>>>>>
>>>>> Cc: Alexey Klimov <alexey.klimov@....com>
>>>>> Cc: Jassi Brar <jaswinder.singh@...aro.org>
>>>>> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
>>>>> ---
>>>>>  drivers/mailbox/mailbox.c | 2 +-
>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
>>>>> index 537f4f6d009b..8da30f833262 100644
>>>>> --- a/drivers/mailbox/mailbox.c
>>>>> +++ b/drivers/mailbox/mailbox.c
>>>>> @@ -351,7 +351,7 @@ struct mbox_chan *mbox_request_channel(struct mbox_client *cl, int index)
>>>>>         init_completion(&chan->tx_complete);
>>>>>
>>>>>         if (chan->txdone_method == TXDONE_BY_POLL && cl->knows_txdone)
>>>>> -               chan->txdone_method |= TXDONE_BY_ACK;
>>>>> +               chan->txdone_method = TXDONE_BY_ACK;
>>>>>
>>>> It has to be restored back in mbox_free_channel()
>>>
>>> Ah right, will fix and repost.
>>>
>>
>> I was too fast to response, I see we already take care of that in free
>> channel. So I think it should be fine as is.
>>
>>         if (chan->txdone_method == (TXDONE_BY_POLL | TXDONE_BY_ACK))
>>                 chan->txdone_method = TXDONE_BY_POLL;
>>
> You were too fast this time :)
> 

Indeed, my understanding was correct before.

> chan->txdone_method == (TXDONE_BY_POLL | TXDONE_BY_ACK)
> 
>   is not same as
> 
> (chan->txdone_method == TXDONE_BY_POLL || chan->txdone_method == TXDONE_BY_ACK)
> 

Ah crap, yes and I have no idea why I thought so when I was about to
change it :(

-- 
Regards,
Sudeep