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Subject: Re: [PATCH] tty: serial: replace spin_lock_irqsave by spin_lock in
 hard IRQ
To:     Johan Hovold <johan@kernel.org>, Tian Tao <tiantao6@hisilicon.com>
CC:     <gregkh@linuxfoundation.org>, <jirislaby@kernel.org>,
        <afaerber@suse.de>, <manivannan.sadhasivam@linaro.org>,
        <linux-serial@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>
References: <1605776489-16283-1-git-send-email-tiantao6@hisilicon.com>
 <X7d85DKvisjA3nYv@localhost>
From:   "tiantao (H)" <tiantao6@huawei.com>
Message-ID: <9ce93d7b-f769-58ed-e6bf-95c34bd0123e@huawei.com>
Date:   Fri, 20 Nov 2020 19:25:03 +0800
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?? 2020/11/20 16:23, Johan Hovold д??:
> On Thu, Nov 19, 2020 at 05:01:29PM +0800, Tian Tao wrote:
>> The code has been in a irq-disabled context since it is hard IRQ. There
>> is no necessity to do it again.
>>
>> Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
>> ---
>>   drivers/tty/serial/owl-uart.c | 5 ++---
>>   1 file changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/tty/serial/owl-uart.c b/drivers/tty/serial/owl-uart.c
>> index c149f8c3..472fdaf 100644
>> --- a/drivers/tty/serial/owl-uart.c
>> +++ b/drivers/tty/serial/owl-uart.c
>> @@ -251,10 +251,9 @@ static void owl_uart_receive_chars(struct uart_port *port)
>>   static irqreturn_t owl_uart_irq(int irq, void *dev_id)
>>   {
>>   	struct uart_port *port = dev_id;
>> -	unsigned long flags;
>>   	u32 stat;
>>   
>> -	spin_lock_irqsave(&port->lock, flags);
>> +	spin_lock(&port->lock);
> 
> Same thing here; this will break with forced irq threading (i.e.
> "threadirqs") since the console code can still end up being called from
> interrupt context.
As the following code shows, owl_uart_irq does not run in the irq 
threading context.
  ret = request_irq(port->irq, owl_uart_irq, IRQF_TRIGGER_HIGH,
                         "owl-uart", port);
         if (ret)
                 return ret;

> 
>>   	stat = owl_uart_read(port, OWL_UART_STAT);
>>   
>> @@ -268,7 +267,7 @@ static irqreturn_t owl_uart_irq(int irq, void *dev_id)
>>   	stat |= OWL_UART_STAT_RIP | OWL_UART_STAT_TIP;
>>   	owl_uart_write(port, stat, OWL_UART_STAT);
>>   
>> -	spin_unlock_irqrestore(&port->lock, flags);
>> +	spin_unlock(&port->lock);
>>   
>>   	return IRQ_HANDLED;
>>   }
> 
> Johan
> 
> .
>