[PATCH 2/3] ccw: clarify passing of subchannel id

Make clear that the upper half of the register must be ignored, just
like normal I/O instructions do.

Signed-off-by: Cornelia Huck <>
---
 content.tex |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/content.tex b/content.tex
index 81237a0..b1c4ed1 100644
--- a/content.tex
+++ b/content.tex
@@ -2243,6 +2243,10 @@ GPR  &   Input Value     & Output Value \\
 \hline
 \end{tabular}
 
+The device MUST ignore bits 0-31 (counting from the left) of GPR2.
+This aligns passing the subchannel ID with the way it is passed
+for the existing I/O instructions.
+
 Host cookie is an optional per-virtqueue 64 bit value that can be
 used by the hypervisor to speed up the notification execution.
 For each notification, the output value is returned in GPR2 and
-- 
1.7.9.5