RE: [Uclinux-dist-devel] [PATCH 1/2] mtd: m25p80: Reworkprobing/JEDEC code | linuxppc-dev

quoted

=20

-----Original Message-----
From: uclinux-dist-devel-bounces@blackfin.uclinux.org=20
[mailto:uclinux-dist-devel-bounces@blackfin.uclinux.org] On=20
Behalf Of Anton Vorontsov
Sent: Friday, June 18, 2010 9:32 PM
To: Barry Song
Cc: David Brownell; Artem Bityutskiy;=20
linux-kernel@vger.kernel.org; linuxppc-dev@ozlabs.org;=20
linux-mtd@lists.infradead.org;=20
uclinux-dist-devel@blackfin.uclinux.org; Andrew Morton
Subject: Re: [Uclinux-dist-devel] [PATCH 1/2] mtd: m25p80:=20
Reworkprobing/JEDEC code

On Sat, Jun 12, 2010 at 02:27:12PM +0800, Barry Song wrote:
On Wed, Aug 19, 2009 at 5:46 AM, Anton Vorontsov
[off-list ref] wrote:
Previosly the driver always tried JEDEC probing, assuming=20
that non-JEDEC
chips will return '0'. But truly non-JEDEC chips (like=20
CAT25) won't do
that, their behaviour on RDID command is undefined, so the=20
driver should
not call jedec_probe() for these chips.

Also, be less strict on error conditions, don't fail to=20
probe if JEDEC
found a chip that is different from what platform code=20
told, instead
just print some warnings and use an information obtained=20
via JEDEC. In
This patch caused a problem:
even though the external flash doesn't exist, it will still pass the
probe() and be registerred into kernel and given the partition table.
You may refer to this bug report:
=20
http://blackfin.uclinux.org/gf/project/uclinux-dist/tracker/?ac
tion=3DTrackerItemEdit&tracker_item_id=3D5975&start=3D0

Thanks for the report.

There's little we can do about it. Platform code asked us
to register the device, and JEDEC probing of M25Pxx chips isn't
reliable (thanks to various vendors that make these JEDEC and
non-JEDEC variants), so the best thing we can do is to register
the chip anyway.

OTOH, if the board pulls MISO line up, then the following patch
should help.
Make sense with pullup to keep the value high while external device
doesn't exist.
If this won't work, we'll have to add some flag to the platform
data, i.e. to force JEDEC probing, and not trust platform data.
How about we add a non_jedec flag in platform_data, if the flag is 1, we
let the detection pass even though the ID is 0? Otherwise, we need a
valid ID?

Not-yet-Signed-off-by: Anton Vorontsov [off-list ref]
---

diff --git a/drivers/mtd/devices/m25p80.c=20
b/drivers/mtd/devices/m25p80.c
index 81e49a9..a307929 100644
--- a/drivers/mtd/devices/m25p80.c
+++ b/drivers/mtd/devices/m25p80.c
@@ -16,6 +16,7 @@
 */
=20
#include <linux/init.h>
+#include <linux/errno.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/interrupt.h>
@@ -723,7 +724,7 @@ static const struct spi_device_id=20
*__devinit jedec_probe(struct spi_device *spi)
	if (tmp < 0) {
		DEBUG(MTD_DEBUG_LEVEL0, "%s: error %d reading=20
JEDEC ID\n",
			dev_name(&spi->dev), tmp);
-		return NULL;
+		return ERR_PTR(tmp);
	}
	jedec =3D id[0];
	jedec =3D jedec << 8;
@@ -737,7 +738,7 @@ static const struct spi_device_id=20
*__devinit jedec_probe(struct spi_device *spi)
	 * exist for non-JEDEC chips, but for compatibility=20
they return ID 0.
	 */
	if (jedec =3D=3D 0)
-		return NULL;
+		return ERR_PTR(-EEXIST);
=20
	ext_jedec =3D id[3] << 8 | id[4];
=20
@@ -749,7 +750,7 @@ static const struct spi_device_id=20
*__devinit jedec_probe(struct spi_device *spi)
			return &m25p_ids[tmp];
		}
	}
-	return NULL;
+	return ERR_PTR(-ENODEV);
}
=20
=20
@@ -794,9 +795,11 @@ static int __devinit m25p_probe(struct=20
spi_device *spi)
		const struct spi_device_id *jid;
=20
		jid =3D jedec_probe(spi);
-		if (!jid) {
+		if (IS_ERR(jid) && PTR_ERR(jid) =3D=3D -EEXIST) {
			dev_info(&spi->dev, "non-JEDEC variant of %s\n",
				 id->name);
+		} else if (IS_ERR(jid)) {
+			return PTR_ERR(jid);
		} else if (jid !=3D id) {
			/*
			 * JEDEC knows better, so overwrite=20
platform ID. We
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