linux-kernel - Re: [PATCH v6 02/46] virtio: use u32, not bitmap for features

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Message-ID: <20141129173412.GH22746@redhat.com>
Date:	Sat, 29 Nov 2014 19:34:12 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Cornelia Huck <cornelia.huck@...ibm.com>
Cc:	linux-kernel@...r.kernel.org, David Miller <davem@...emloft.net>,
	rusty@....ibm.com, nab@...ux-iscsi.org, pbonzini@...hat.com,
	thuth@...ux.vnet.ibm.com, dahi@...ux.vnet.ibm.com,
	Rusty Russell <rusty@...tcorp.com.au>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Amit Shah <amit.shah@...hat.com>,
	Ohad Ben-Cohen <ohad@...ery.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	linux390@...ibm.com, Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Ashutosh Dixit <ashutosh.dixit@...el.com>,
	Nikhil Rao <nikhil.rao@...el.com>,
	Siva Yerramreddy <yshivakrishna@...il.com>,
	Joel Stanley <joel@....id.au>,
	virtualization@...ts.linux-foundation.org, lguest@...ts.ozlabs.org,
	linux-s390@...r.kernel.org
Subject: Re: [PATCH v6 02/46] virtio: use u32, not bitmap for features

On Fri, Nov 28, 2014 at 01:44:57PM +0100, Cornelia Huck wrote:
> On Thu, 27 Nov 2014 22:07:41 +0200
> "Michael S. Tsirkin" <mst@...hat.com> wrote:
> 
> > It seemed like a good idea to use bitmap for features
> > in struct virtio_device, but it's actually a pain,
> > and seems to become even more painful when we get more
> > than 32 feature bits.  Just change it to a u32 for now.
> > 
> > Based on patch by Rusty.
> > 
> > Suggested-by: David Hildenbrand <dahi@...ux.vnet.ibm.com>
> > Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
> > Signed-off-by: Cornelia Huck <cornelia.huck@...ibm.com>
> > Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> 
> > diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
> > index d34ebfa..ab95a4c 100644
> > --- a/drivers/virtio/virtio_pci.c
> > +++ b/drivers/virtio/virtio_pci.c
> > @@ -120,8 +120,7 @@ static void vp_finalize_features(struct virtio_device *vdev)
> >  	vring_transport_features(vdev);
> > 
> >  	/* We only support 32 feature bits. */
> 
> I think you can kill this comment...

Why? It's still true for virtio pci at this point, that's why we
just do iowrite32 here.

> > -	BUILD_BUG_ON(ARRAY_SIZE(vdev->features) != 1);
> > -	iowrite32(vdev->features[0], vp_dev->ioaddr+VIRTIO_PCI_GUEST_FEATURES);
> > +	iowrite32(vdev->features, vp_dev->ioaddr+VIRTIO_PCI_GUEST_FEATURES);
> 
> ...and add blanks around '+', as you're touching this line anyway.
> 
> >  }
> > 
> >  /* virtio config->get() implementation */
> 
> Reviewed-by: Cornelia Huck <cornelia.huck@...ibm.com>
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