linux-kernel - [PATCH 4.4 015/113] libnvdimm, nd_blk: mask off reserved status bits

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Message-Id: <20160905164349.868913239@linuxfoundation.org>
Date:   Mon,  5 Sep 2016 18:43:38 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, "Lee, Chun-Yi" <jlee@...e.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: [PATCH 4.4 015/113] libnvdimm, nd_blk: mask off reserved status bits

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ross Zwisler <ross.zwisler@...ux.intel.com>

commit 68202c9f0ad6e16ee806fbadbc5838d55fe5aa5c upstream.

The "NVDIMM Block Window Driver Writer's Guide":

    http://pmem.io/documents/NVDIMM_DriverWritersGuide-July-2016.pdf

...defines the layout of the block window status register.  For the July
2016 version of the spec linked to above, this happens in Figure 4 on
page 26.

The only bits defined in this spec are bits 31, 5, 4, 2, 1 and 0.  The
rest of the bits in the status register are reserved, and there is a
warning following the diagram that says:

    Note: The driver cannot assume the value of the RESERVED bits in the
    status register are zero. These reserved bits need to be masked off, and
    the driver must avoid checking the state of those bits.

This change ensures that for hardware implementations that set these
reserved bits in the status register, the driver won't incorrectly fail the
block I/Os.

Reviewed-by: Lee, Chun-Yi <jlee@...e.com>
Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/acpi/nfit.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/acpi/nfit.c
+++ b/drivers/acpi/nfit.c
@@ -1072,11 +1072,12 @@ static u32 read_blk_stat(struct nfit_blk
 {
 	struct nfit_blk_mmio *mmio = &nfit_blk->mmio[DCR];
 	u64 offset = nfit_blk->stat_offset + mmio->size * bw;
+	const u32 STATUS_MASK = 0x80000037;
 
 	if (mmio->num_lines)
 		offset = to_interleave_offset(offset, mmio);
 
-	return readl(mmio->addr.base + offset);
+	return readl(mmio->addr.base + offset) & STATUS_MASK;
 }
 
 static void write_blk_ctl(struct nfit_blk *nfit_blk, unsigned int bw,