VIRTIO Spec feedback #2 From: Thomas Huth

Two patches: diff --git a/content.tex b/content.tex index 803615d..4ebc4b1 100644 — a/content.tex +++ b/content.tex @@ -801,9 +801,10 @@ any Revision ID value. \subsection {PCI Device Layout} \label {sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout} -To configure the device, -use I/O and/or memory regions and/or PCI configuration space of the PCI device. -These contain the virtio header registers, the notification register, the +The device is configured via I/O and/or memory regions (though see +VIRTIO_PCI_CAP_PCI_CFG for access via the PCI configuration space). + +These regions contain the virtio header registers, the notification register, the ISR status register and device specific registers, as specified by Virtio Structure PCI Capabilities. @@ -847,8 +848,7 @@ Common configuration structure layout is documented below: \begin {description} \item [device_feature_select] The driver uses this to select which Feature Bits the device_feature field shows. Value 0x0 selects Feature Bits 0 to 31 Value 0x1 selects Feature Bits 32 to 63 + Value 0x0 selects Feature Bits 0 to 31, 0x1 selects Feature Bits 32 to 63. The device MUST present 0 on device_feature for any other value. \item [device_feature] @@ -857,8 +857,7 @@ Common configuration structure layout is documented below: \item [driver_feature_select] The driver uses this to select which Feature Bits the driver_feature field shows. Value 0x0 selects Feature Bits 0 to 31 Value 0x1 selects Feature Bits 32 to 63 + Value 0x0 selects Feature Bits 0 to 31, 0x1 selects Feature Bits 32 to 63. When set to any other value, reads from driver_feature return 0, writing 0 into driver_feature has no effect. The driver MUST not write any other value into driver_feature (a corollary of @@ -899,7 +898,7 @@ Common configuration structure layout is documented below: \item [queue_enable] The driver uses this to selectively prevent the device from executing requests from this virtqueue. 1 - enabled; 0 - disabled + 1 - enabled; 0 - disabled. The driver MUST configure the other virtqueue fields before enabling the virtqueue. @@ -1043,7 +1042,7 @@ read-only: }; \end {lstlisting} -This structure can optionally followed by extra data, depending on +This structure can optionally be followed by extra data, depending on other fields, as documented below. Note that future versions of this specification will likely @@ -1369,10 +1368,13 @@ following sections. \subsection{MMIO Device Discovery}\label{sec:Virtio Transport Options / Virtio Over MMIO / MMIO Device Discovery} -Unlike PCI, MMIO provides no generic device discovery. For -systems using Flattened Device Trees the suggested format is: +Unlike PCI, MMIO provides no generic device discovery. For each +device, the guest OS will need to know the location of the registers +and interrupt(s) used. The suggested binding for systems using +flattened device trees is shown in this example: \begin{lstlisting} + // EXAMPLE: virtio_block device taking 256 bytes at 0x1e000, interrupt 42. virtio_block@1e000 { compatible = "virtio,mmio"; reg = <0x1e000 0x100>; @@ -1941,7 +1943,7 @@ revision & length & data & remarks \hline \end {tabular} -Note that a change in the virtio standard does not neccessarily +Note that a change in the virtio standard does not necessarily correspond to a change in the virtio-ccw revision. A device MUST post a unit check with command reject for any revision @@ -2037,7 +2039,7 @@ and align the alignment. \subsubsection{Virtqueue Layout}\label{sec:Virtio Transport Options / Virtio over channel I/O / Device Initialization / Virtqueue Layout} -The virtqueue is physically contiguous, with padded added to make the +The virtqueue is physically contiguous, with padding added to make the used ring meet the align value: \begin{tabular} {|l|l|l|} Subject: [PATCH 1/1] virtio-ccw: clarifications further qualify bit numbering specify summary indicator contents drop early printk spec; it is only a hack that was never used upstream Reported-by: Thomas Huth <thuth@linux.vnet.ibm.com> Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com> — content.tex | 10 +++------- 1 file changed, 3 insertions , 7 deletions diff --git a/content.tex b/content.tex index 803615d..0a94c07 100644 — a/content.tex +++ b/content.tex @@ -2174,7 +2174,8 @@ summary_indicator contains the guest address of the 8 bit summary indicator. indicator contains the guest address of an area wherin the indicators for the devices are contained, starting at bit_nr, one bit per -virtqueue of the device. Bit numbers start at the left. +virtqueue of the device. Bit numbers start at the left, i.e. the most +significant bit in the first byte is assigned the bit number 0. isc contains the I/O interruption subclass to be used for the adapter I/O interrupt. It may be different from the isc used by the proxy virtio-ccw device's subchannel. @@ 2224,7 +2225,7 @@ host >guest notification about virtqueue activity. For notifying the driver of virtqueue buffers, the device sets the bit in the guest-provided indicator area at the corresponding offset. -The guest-provided summary indicator is also set. An adapter I/O +The guest-provided summary indicator is set to 0x01. An adapter I/O interrupt for the corresponding interruption subclass is generated. The device SHOULD only generate an adapter I/O interrupt if the summary indicator had not been set prior to notification. The driver @@ -2273,11 +2274,6 @@ should be passed in GPR4 for the next notification: info->cookie); \end {lstlisting} -\subsubsection {Early printk for Virtio Consoles} \label {sec:Virtio Transport Options / Virtio over channel I/O / Device Operation / Early printk for Virtio Consoles} - -For the early printk mechanism, diagnose 0x500 with subcode 0 is -used. - \subsubsection {Resetting Devices} \label {sec:Virtio Transport Options / Virtio over channel I/O / Device Operation / Resetting Devices} In order to reset a device, a driver sends the