[PATCH] spi: intel: only check locked opmenu for SW sequencer operations

[Rosen Penev <rosenp@gmail.com>]

On controllers that use the software sequencer for register access (LPT
and BYT), intel_spi_supports_mem_op() rejects any operation whose opcode
is not in the BIOS-locked OPMENU. However the check is applied to every
operation, including normal data reads and writes which are always
executed by the hardware sequencer and never consult the OPMENU.

On a Dell Precision M4800 (Lynx Point) the BIOS locks OPMENU to
{02, 3b, 20, 05, 9f, 9f, 00, 00}, which lacks both READ (0x03) and
FAST_READ (0x0b). As a result every read op is rejected and spi-nor
fails to probe both flash components:

  intel-spi intel-spi: 0x3 not supported
  intel-spi intel-spi: 0xb not supported
  spi-nor spi0.0: can't select read settings supported by both the SPI controller and memory.
  spi-nor spi0.0: probe with driver spi-nor failed with error -22

Only enforce the OPMENU check for operations that actually go through
the software sequencer: register reads/writes when swseq_reg is set and
erase when swseq_erase is set. With this both flash chips (W25Q64 and
W25Q32) probe and read back correctly.

Fixes: e23e5a05d1fd ("mtd: spi-nor: intel-spi: Convert to SPI MEM")
Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
 drivers/spi/spi-intel.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi-intel.c b/drivers/spi/spi-intel.c
index 7494b921a743..6f1414b199e6 100644
--- a/drivers/spi/spi-intel.c
+++ b/drivers/spi/spi-intel.c
@@ -754,6 +754,18 @@ intel_spi_match_mem_op(struct intel_spi *ispi, const struct spi_mem_op *op)
 	return NULL;
 }
 
+static bool intel_spi_op_uses_swseq(const struct intel_spi *ispi,
+				    const struct intel_spi_mem_op *iop)
+{
+	if (iop->exec_op == intel_spi_read_reg ||
+	    iop->exec_op == intel_spi_write_reg)
+		return ispi->swseq_reg;
+	if (iop->exec_op == intel_spi_erase)
+		return ispi->swseq_erase;
+	/* Data reads and writes always use the HW sequencer */
+	return false;
+}
+
 static bool intel_spi_supports_mem_op(struct spi_mem *mem,
 				      const struct spi_mem_op *op)
 {
@@ -768,9 +780,11 @@ static bool intel_spi_supports_mem_op(struct spi_mem *mem,
 
 	/*
 	 * For software sequencer check that the opcode is actually
-	 * present in the opmenu if it is locked.
+	 * present in the opmenu if it is locked. Operations executed by
+	 * the hardware sequencer do not use the opmenu so skip the check
+	 * for them.
 	 */
-	if (ispi->swseq_reg && ispi->locked) {
+	if (ispi->locked && intel_spi_op_uses_swseq(ispi, iop)) {
 		int i;
 
 		/* Check if it is in the locked opcodes list */
-- 
2.56.0