ata_timing: ensure t->cycle is always correct

Russell King hit a case where quantisation errors accumulated such that
the cycle time was shorter than rather than equal to the active/recovery
time. The code already knows how to stretch times to fit the cycle time
but does not know about the reverse.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 227399e4847..4e1df5382b9 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -2639,6 +2639,12 @@ int ata_timing_compute(struct ata_device *adev, unsigned short speed,
                 t->active += (t->cycle - (t->active + t->recover)) / 2;
                 t->recover = t->cycle - t->active;
         }
+        
+        /* In a few cases quantisation may produce enough errors to
+           leave t->cycle too low for the sum of active and recovery
+           if so we must correct this */
+        if (t->active + t->recover > t->cycle)
+                t->cycle = t->active + t->recover;
 
         return 0;
 }