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Subject: Re: [virtio] [PATCH v5] virtio-blk: restore VIRTIO_BLK_F_FLUSH and VIRTIO_BLK_F_CONFIG_WCE
On Tue, 11 Aug 2015 16:23:39 +0300 "Michael S. Tsirkin" <mst@redhat.com> wrote: > OK to summarize, how about: > > In free text: > > The cache mode after reset can be either writeback or writethrough. > The actual mode can be determined by reading \field{writeback}. > > In conformance paragraph: > > The driver MUST NOT read \field{writeback} before setting > the FEATURES_OK \field{status} bit. > > > And in legacy section: > > Legacy drivers and drivers did not support the FEATURES_OK \field{status} bit, > and used the device before setting the DRIVER_OK bit. > Therefore: > > When using the legacy interface, the driver MAY read \field{writeback} > before setting the FEATURES_OK \field{status} field. But if it is using the legacy interface, it won't ever set FEATURES_OK, no? The wording is a bit confusing. "As the legacy interface did not support FEATURES_OK to signal end of feature negotation, the driver MAY read \field{writeback} without the FEATURES_OK \field{status} bit having been set." ? Do we need to mandate that the device MUST assume the driver is operating in legacy mode in that case? > When using the legacy interface, the transitional devices MAY assume > that driver features won't be changed after reading \field{writeback}. "For a driver using the legacy interface, the transitional device MAY assume that the driver won't change features after reading \field{writeback}." ?
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