linux-kernel - Re: [PATCH 5/5] virtio: don't require a config space on the console device.

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Date:	Mon, 09 Feb 2015 10:26:29 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Amit Shah <amit.shah@...hat.com>
Subject: Re: [PATCH 5/5] virtio: don't require a config space on the console device.

"Michael S. Tsirkin" <mst@...hat.com> writes:
> On Fri, Feb 06, 2015 at 03:36:56PM +1030, Rusty Russell wrote:
>> Strictly, it's only needed when we have features (size or multiport).
>> 
>> Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
>> ---
>>  drivers/char/virtio_console.c | 12 ++++++++----
>>  1 file changed, 8 insertions(+), 4 deletions(-)
>> 
>> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
>> index 26afb56a8073..8f182b0015b5 100644
>> --- a/drivers/char/virtio_console.c
>> +++ b/drivers/char/virtio_console.c
>> @@ -1986,10 +1986,14 @@ static int virtcons_probe(struct virtio_device *vdev)
>>  	bool multiport;
>>  	bool early = early_put_chars != NULL;
>>  
>> -	if (!vdev->config->get) {
>> -		dev_err(&vdev->dev, "%s failure: config access disabled\n",
>> -			__func__);
>> -		return -EINVAL;
>> +	/* We only need a config space if features are offered */
>> +	if (virtio_has_feature(vdev, VIRTIO_CONSOLE_F_SIZE)
>> +	    || virtio_has_feature(vdev, VIRTIO_CONSOLE_F_MULTIPORT)) {
>> +		if (!vdev->config->get) {
>
> I dislike nested ifs. How about
> 		if (!vdev->config->get && (
> 		    (virtio_has_feature(vdev, VIRTIO_CONSOLE_F_SIZE)
> 		    || virtio_has_feature(vdev, VIRTIO_CONSOLE_F_MULTIPORT))

OK, fixed.

Thanks,
Rusty.

virtio: don't require a config space on the console device.

Strictly, it's only needed when we have features (size or multiport).

Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 26afb56a8073..fae2dbbf5745 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -1986,7 +1986,10 @@ static int virtcons_probe(struct virtio_device *vdev)
 	bool multiport;
 	bool early = early_put_chars != NULL;
 
-	if (!vdev->config->get) {
+	/* We only need a config space if features are offered */
+	if (!vdev->config->get &&
+	    (virtio_has_feature(vdev, VIRTIO_CONSOLE_F_SIZE)
+	     || virtio_has_feature(vdev, VIRTIO_CONSOLE_F_MULTIPORT))) {
 		dev_err(&vdev->dev, "%s failure: config access disabled\n",
 			__func__);
 		return -EINVAL;
--
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