Re: [Xen-devel] [PATCH] ns16550: Re-order the serial port address checking

From: Wei Xu <xuwei5@hisilicon.com>
To: Julien Grall <julien@xen.org>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	"Zengtao \(B\)" <prime.zeng@hisilicon.com>, Wei Liu <wl@xen.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	George Dunlap <George.Dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	Linuxarm <linuxarm@huawei.com>,
	Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>,
	Jan Beulich <jbeulich@suse.com>
Subject: Re: [Xen-devel] [PATCH] ns16550: Re-order the serial port address checking
Date: Tue, 25 Feb 2020 08:33:47 +0800	[thread overview]
Message-ID: <5E546B6B.70906@hisilicon.com> (raw)
In-Reply-To: <8bb7d100-0ca4-c0f9-b294-f2e7a173e1c9@xen.org>

Hi Julien,

On 2020/2/25 6:03, Julien Grall wrote:
> Hi Wei,
> 
> Thank you for sending a follow-up.
> 
> On 24/02/2020 11:30, Wei Xu wrote:
>> Check the serial port address space before checking the address.
> 
> Could you explain in a sentence why you want to re-order?

Do you think is it OK to explain as following:

The serial port address space ID qualifies the address.
Whether a value of zero for the serial port address can sensibly
mean "disabled" depends on the address space ID. Hence check the
address space ID before checking the address.

Thanks!

Best Regards,
Wei

> 
> Cheers,
> 
>>
>> Signed-off-by: Wei Xu <xuwei5@hisilicon.com>
>> ---
>>   xen/drivers/char/ns16550.c | 12 ++++++------
>>   1 file changed, 6 insertions(+), 6 deletions(-)
>>
>> diff --git a/xen/drivers/char/ns16550.c b/xen/drivers/char/ns16550.c
>> index dc8ac4c..425e044 100644
>> --- a/xen/drivers/char/ns16550.c
>> +++ b/xen/drivers/char/ns16550.c
>> @@ -1644,6 +1644,12 @@ static int __init ns16550_acpi_uart_init(const void *data)
>>
>>       spcr = container_of(table, struct acpi_table_spcr, header);
>>
>> +    if ( unlikely(spcr->serial_port.space_id != ACPI_ADR_SPACE_SYSTEM_MEMORY) )
>> +    {
>> +        printk("ns16550: Address space type is not mmio\n");
>> +        return -EINVAL;
>> +    }
>> +
>>       /*
>>        * The serial port address may be 0 for example
>>        * if the console redirection is disabled.
>> @@ -1654,12 +1660,6 @@ static int __init ns16550_acpi_uart_init(const void *data)
>>           return -EINVAL;
>>       }
>>
>> -    if ( unlikely(spcr->serial_port.space_id != ACPI_ADR_SPACE_SYSTEM_MEMORY) )
>> -    {
>> -        printk("ns16550: Address space type is not mmio\n");
>> -        return -EINVAL;
>> -    }
>> -
>>       ns16550_init_common(uart);
>>
>>       /*
>>
> 

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