ioat: ignore reserved bits for chancnt and xfercap

Don't trust that the reserved bits are always zero, also sanity check
the returned value.

Signed-off-by: Maciej Sosnowski <maciej.sosnowski@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/dma/ioat/dma.c b/drivers/dma/ioat/dma.c
index 08417ad4edca..5173ba97ba31 100644
--- a/drivers/dma/ioat/dma.c
+++ b/drivers/dma/ioat/dma.c
@@ -132,7 +132,14 @@ static int ioat1_enumerate_channels(struct ioatdma_device *device)
 
         INIT_LIST_HEAD(&dma->channels);
         dma->chancnt = readb(device->reg_base + IOAT_CHANCNT_OFFSET);
+        dma->chancnt &= 0x1f; /* bits [4:0] valid */
+        if (dma->chancnt > ARRAY_SIZE(device->idx)) {
+                dev_warn(dev, "(%d) exceeds max supported channels (%zu)\n",
+                         dma->chancnt, ARRAY_SIZE(device->idx));
+                dma->chancnt = ARRAY_SIZE(device->idx);
+        }
         xfercap_scale = readb(device->reg_base + IOAT_XFERCAP_OFFSET);
+        xfercap_scale &= 0x1f; /* bits [4:0] valid */
         xfercap = (xfercap_scale == 0 ? -1 : (1UL << xfercap_scale));
         dev_dbg(dev, "%s: xfercap = %d\n", __func__, xfercap);