Re: [PATCH 17/23] mtd: spi-nor: Fix clearing of QE bit on lock()/unlock()

Hi, Vignesh,

On 09/19/2019 05:33 PM, Vignesh Raghavendra wrote:

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Hi Tudor

[...]

On 17-Sep-19 9:25 PM, Tudor.Ambarus@microchip.com wrote:

quoted

+static int spi_nor_write_16bit_sr_and_check(struct spi_nor *nor, u8 status_new,
+					    u8 mask)
+{
+	int ret;
+	u8 *sr_cr = nor->bouncebuf;
+	u8 cr_written;
+
+	/* Make sure we don't overwrite the contents of Status Register 2. */
+	if (!(nor->flags & SNOR_F_NO_READ_CR)) {

Assuming SNOR_F_NO_READ_CR is not set...

quoted

+		ret = spi_nor_read_cr(nor, &sr_cr[1]);
+		if (ret)
+			return ret;
+	} else if (nor->flash.quad_enable) {
+		/*
+		 * If the Status Register 2 Read command (35h) is not
+		 * supported, we should at least be sure we don't
+		 * change the value of the SR2 Quad Enable bit.
+		 *
+		 * We can safely assume that when the Quad Enable method is
+		 * set, the value of the QE bit is one, as a consequence of the
+		 * nor->flash.quad_enable() call.
+		 *
+		 * We can safely assume that the Quad Enable bit is present in
+		 * the Status Register 2 at BIT(1). According to the JESD216
+		 * revB standard, BFPT DWORDS[15], bits 22:20, the 16-bit
+		 * Write Status (01h) command is available just for the cases
+		 * in which the QE bit is described in SR2 at BIT(1).
+		 */
+		sr_cr[1] = CR_QUAD_EN_SPAN;
+	} else {
+		sr_cr[1] = 0;
+	}
+

CR_QUAD_EN_SPAN will not be in sr_cr[1] when we reach here. So code
won't enable quad mode.

I get the problem now. spi_nor_write_16bit_sr_and_check() does not modify the
value of the QE bit, which is good in the lock/unlock() case. We want to
lock/unlock() without enabling or disabling the Quad Mode.

As you found, the problem comes later in spi_nor_sr2_bit1_quad_enable() because
I use there spi_nor_write_16bit_sr_and_check() which keeps the value of the QE
bit, without setting it to one, so the spi_nor_sr2_bit1_quad_enable() did not
enable the Quad Mode if not previously enabled.

What I'll do is to introduce a new argument to:
static int spi_nor_write_16bit_sr_and_check(struct spi_nor *nor, u8 status_new,
					    u8 mask, bool set_quad_enable)

and do a
if (set_quad_enable)
	sr_cr[1] |= CR_QUAD_EN_SPAN;
after initializing sr_cr[1]

The lock/unlock() methods will call the function with set_quad_enable being
false (we don't want to modify the QE value), and the
spi_nor_sr2_bit1_quad_enable() will call it with set_quad_enable being true, we
want to set QE to one (we don't care of the QE bit previous value).

We'll avoid code duplication, lock/unlock() and spi_nor_sr2_bit1_quad_enable()
calling the same method.

Cheers,
ta
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