linux-kernel - RE: [PATCH] virtio_pci: Wait for legacy device to be reset

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Message-ID: <TY2PR06MB34242144FB4F944DD866567B859A9@TY2PR06MB3424.apcprd06.prod.outlook.com>
Date:   Tue, 11 Apr 2023 06:39:16 +0000
From:   Angus Chen <angus.chen@...uarmicro.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
CC:     "jasowang@...hat.com" <jasowang@...hat.com>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] virtio_pci: Wait for legacy device to be reset

Hi mst.

> -----Original Message-----
> From: Michael S. Tsirkin <mst@...hat.com>
> Sent: Tuesday, April 11, 2023 2:30 PM
> To: Angus Chen <angus.chen@...uarmicro.com>
> Cc: jasowang@...hat.com; virtualization@...ts.linux-foundation.org;
> linux-kernel@...r.kernel.org
> Subject: Re: [PATCH] virtio_pci: Wait for legacy device to be reset
> 
> On Tue, Apr 11, 2023 at 09:38:32AM +0800, Angus Chen wrote:
> > We read the status of device after reset,
> > It is not guaranteed that the device be reseted successfully.
> 
> Sorry not guaranteed by what? I am guessing you have a legacy device
> that does not reset fully on write, and you need to wait?
 When the card not finished reset, the read only return the middle state of card.
> 
> > We can use a while loop to make sure that,like the modern device did.
> > The spec is not request it ,but it work.
> >
> > Signed-off-by: Angus Chen <angus.chen@...uarmicro.com>
> 
> Generally I don't much like touching legacy, no telling what
> that will do. Case in point, is your device a pure
> legacy device or a transitional device?
 Yes.,we have a real card which is use vitio spec.
 Thank you.
> 
> > ---
> >  drivers/virtio/virtio_pci_legacy.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/virtio/virtio_pci_legacy.c b/drivers/virtio/virtio_pci_legacy.c
> > index 2257f1b3d8ae..f2d241563e4f 100644
> > --- a/drivers/virtio/virtio_pci_legacy.c
> > +++ b/drivers/virtio/virtio_pci_legacy.c
> > @@ -14,6 +14,7 @@
> >   *  Michael S. Tsirkin <mst@...hat.com>
> >   */
> >
> > +#include <linux/delay.h>
> >  #include "linux/virtio_pci_legacy.h"
> >  #include "virtio_pci_common.h"
> >
> > @@ -97,7 +98,8 @@ static void vp_reset(struct virtio_device *vdev)
> >  	vp_legacy_set_status(&vp_dev->ldev, 0);
> >  	/* Flush out the status write, and flush in device writes,
> >  	 * including MSi-X interrupts, if any. */
> > -	vp_legacy_get_status(&vp_dev->ldev);
> > +	while (vp_legacy_get_status(&vp_dev->ldev))
> > +		msleep(1);
> 
> The problem with this is that it will break surprise
> removal even worse than it's already broken.
> 
> 
> >  	/* Flush pending VQ/configuration callbacks. */
> >  	vp_synchronize_vectors(vdev);
> >  }
> > --
> > 2.25.1