[PATCH v5 0/2] at24: support eeproms that do not auto-rollover reads.

[PATCH v5 0/2] at24: support eeproms that do not auto-rollover reads.

[Sven Van Asbroeck]

v5:
	at Rob Herring's request, renamed devicetree property:
		at24,no-read-rollover -> no-read-rollover

v4:
	renamed devicetree property:
		no-read-rollover -> at24,no-read-rollover
	dt-bindings update now a separate patch

v3:
	rebased against at24 maintainer's devel staging branch:
	git://git.kernel.org/pub/scm/linux/kernel/git/brgl/linux.git at24/devel
	clarified some of the comments and wording

v2:
	kbuild test robot feedback: correct
		"warning: comparison of distinct pointer types lacks a cast"
	build warning on some compilers / architectures.

v1:
	original patch

Sven Van Asbroeck (2):
  at24: support eeproms that do not auto-rollover reads.
  dt-bindings: add eeprom "at24,no-read-rollover" property

 .../devicetree/bindings/eeprom/eeprom.txt          |  5 +++
 drivers/misc/eeprom/at24.c                         | 37 +++++++++++++++-------
 include/linux/platform_data/at24.h                 |  2 ++
 3 files changed, 32 insertions(+), 12 deletions(-)

-- 
1.9.1

[PATCH v5 1/2] at24: support eeproms that do not auto-rollover reads.

[Sven Van Asbroeck]

Some multi-address eeproms in the at24 family may not automatically
roll-over reads to the next slave address. On those eeproms, reads
that straddle slave boundaries will not work correctly.

Solution:
Mark such eeproms with a flag that prevents reads straddling
slave boundaries. Add the AT24_FLAG_NO_RDROL flag to the eeprom
entry in the device_id table, or add 'no-read-rollover' to the
eeprom devicetree entry.

Note that I have not personally enountered an at24 chip that
does not support read rollovers. They may or may not exist.
However, my hardware requires this functionality because of
a quirk.

It's up to the Linux community to decide if this patch is useful/
general enough to warrant merging.

Signed-off-by: Sven Van Asbroeck <svendev@arcx.com>
---
 drivers/misc/eeprom/at24.c         | 37 +++++++++++++++++++++++++------------
 include/linux/platform_data/at24.h |  2 ++
 2 files changed, 27 insertions(+), 12 deletions(-)

diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index 625b001..8c93ed0 100644
--- a/drivers/misc/eeprom/at24.c
+++ b/drivers/misc/eeprom/at24.c
@@ -251,15 +251,6 @@ struct at24_data {
  * Slave address and byte offset derive from the offset. Always
  * set the byte address; on a multi-master board, another master
  * may have changed the chip's "current" address pointer.
- *
- * REVISIT some multi-address chips don't rollover page reads to
- * the next slave address, so we may need to truncate the count.
- * Those chips might need another quirk flag.
- *
- * If the real hardware used four adjacent 24c02 chips and that
- * were misconfigured as one 24c08, that would be a similar effect:
- * one "eeprom" file not four, but larger reads would fail when
- * they crossed certain pages.
  */
 static struct at24_client *at24_translate_offset(struct at24_data *at24,
 						 unsigned int *offset)
@@ -277,6 +268,28 @@ static struct at24_client *at24_translate_offset(struct at24_data *at24,
 	return &at24->client[i];
 }
 
+static size_t at24_adjust_read_count(struct at24_data *at24,
+				      unsigned int offset, size_t count)
+{
+	unsigned int bits;
+	size_t remainder;
+	/*
+	 * In case of multi-address chips that don't rollover reads to
+	 * the next slave address: truncate the count to the slave boundary,
+	 * so that the read never straddles slaves.
+	 */
+	if (at24->chip.flags & AT24_FLAG_NO_RDROL) {
+		bits = (at24->chip.flags & AT24_FLAG_ADDR16) ? 16 : 8;
+		remainder = BIT(bits) - offset;
+		if (count > remainder)
+			count = remainder;
+	}
+	if (count > io_limit)
+		count = io_limit;
+
+	return count;
+}
+
 static ssize_t at24_regmap_read(struct at24_data *at24, char *buf,
 				unsigned int offset, size_t count)
 {
@@ -289,9 +302,7 @@ static ssize_t at24_regmap_read(struct at24_data *at24, char *buf,
 	at24_client = at24_translate_offset(at24, &offset);
 	regmap = at24_client->regmap;
 	client = at24_client->client;
-
-	if (count > io_limit)
-		count = io_limit;
+	count = at24_adjust_read_count(at24, offset, count);
 
 	/* adjust offset for mac and serial read ops */
 	offset += at24->offset_adj;
@@ -457,6 +468,8 @@ static void at24_get_pdata(struct device *dev, struct at24_platform_data *chip)
 
 	if (device_property_present(dev, "read-only"))
 		chip->flags |= AT24_FLAG_READONLY;
+	if (device_property_present(dev, "no-read-rollover"))
+		chip->flags |= AT24_FLAG_NO_RDROL;
 
 	err = device_property_read_u32(dev, "size", &val);
 	if (!err)
diff --git a/include/linux/platform_data/at24.h b/include/linux/platform_data/at24.h
index 271a4e2..841bb28 100644
--- a/include/linux/platform_data/at24.h
+++ b/include/linux/platform_data/at24.h
@@ -50,6 +50,8 @@ struct at24_platform_data {
 #define AT24_FLAG_TAKE8ADDR	BIT(4)	/* take always 8 addresses (24c00) */
 #define AT24_FLAG_SERIAL	BIT(3)	/* factory-programmed serial number */
 #define AT24_FLAG_MAC		BIT(2)	/* factory-programmed mac address */
+#define AT24_FLAG_NO_RDROL  BIT(1)	/* does not auto-rollover reads to */
+					/* the next slave address */
 
 	void		(*setup)(struct nvmem_device *nvmem, void *context);
 	void		*context;
-- 
1.9.1

[PATCH v5 2/2] dt-bindings: add eeprom "no-read-rollover" property

[Sven Van Asbroeck]

Adds an optional property for at24 eeproms.
This parameterless property indicates that the multi-address eeprom
does not automatically roll over reads to the next slave address.

Signed-off-by: Sven Van Asbroeck <svendev@arcx.com>
---
 Documentation/devicetree/bindings/eeprom/eeprom.txt | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Documentation/devicetree/bindings/eeprom/eeprom.txt b/Documentation/devicetree/bindings/eeprom/eeprom.txt
index 27f2bc1..5bfc0ac 100644
--- a/Documentation/devicetree/bindings/eeprom/eeprom.txt
+++ b/Documentation/devicetree/bindings/eeprom/eeprom.txt
@@ -38,6 +38,11 @@ Optional properties:
 
   - size: total eeprom size in bytes
 
+  - no-read-rollover:
+			This parameterless property indicates that the multi-address
+			eeprom does not automatically roll over reads to the next
+			slave address. Please consult the manual of your device.
+
 Example:
 
 eeprom@52 {
-- 
1.9.1

Re: [PATCH v5 2/2] dt-bindings: add eeprom "no-read-rollover" property

[Rob Herring]

On Thu, Dec 7, 2017 at 8:36 AM, Sven Van Asbroeck <svendev@arcx.com> wrote:
> Adds an optional property for at24 eeproms.
> This parameterless property indicates that the multi-address eeprom
> does not automatically roll over reads to the next slave address.
>
> Signed-off-by: Sven Van Asbroeck <svendev@arcx.com>
> ---
>  Documentation/devicetree/bindings/eeprom/eeprom.txt | 5 +++++
>  1 file changed, 5 insertions(+)

Reviewed-by: Rob Herring <robh@kernel.org>

Re: [PATCH v5 1/2] at24: support eeproms that do not auto-rollover reads.

[Bartosz Golaszewski]

2017-12-07 15:36 GMT+01:00 Sven Van Asbroeck <svendev@arcx.com>:
> Some multi-address eeproms in the at24 family may not automatically
> roll-over reads to the next slave address. On those eeproms, reads
> that straddle slave boundaries will not work correctly.
>
> Solution:
> Mark such eeproms with a flag that prevents reads straddling
> slave boundaries. Add the AT24_FLAG_NO_RDROL flag to the eeprom
> entry in the device_id table, or add 'no-read-rollover' to the
> eeprom devicetree entry.
>
> Note that I have not personally enountered an at24 chip that
> does not support read rollovers. They may or may not exist.
> However, my hardware requires this functionality because of
> a quirk.
>
> It's up to the Linux community to decide if this patch is useful/
> general enough to warrant merging.
>
> Signed-off-by: Sven Van Asbroeck <svendev@arcx.com>
> ---
>  drivers/misc/eeprom/at24.c         | 37 +++++++++++++++++++++++++------------
>  include/linux/platform_data/at24.h |  2 ++
>  2 files changed, 27 insertions(+), 12 deletions(-)
>

Hi Sven,

looks good in general, just a couple nits to fix below and it can be applied.

> diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
> index 625b001..8c93ed0 100644
> --- a/drivers/misc/eeprom/at24.c
> +++ b/drivers/misc/eeprom/at24.c
> @@ -251,15 +251,6 @@ struct at24_data {
>   * Slave address and byte offset derive from the offset. Always
>   * set the byte address; on a multi-master board, another master
>   * may have changed the chip's "current" address pointer.
> - *
> - * REVISIT some multi-address chips don't rollover page reads to
> - * the next slave address, so we may need to truncate the count.
> - * Those chips might need another quirk flag.
> - *
> - * If the real hardware used four adjacent 24c02 chips and that
> - * were misconfigured as one 24c08, that would be a similar effect:
> - * one "eeprom" file not four, but larger reads would fail when
> - * they crossed certain pages.
>   */
>  static struct at24_client *at24_translate_offset(struct at24_data *at24,
>                                                  unsigned int *offset)
> @@ -277,6 +268,28 @@ static struct at24_client *at24_translate_offset(struct at24_data *at24,
>         return &at24->client[i];
>  }
>
> +static size_t at24_adjust_read_count(struct at24_data *at24,
> +                                     unsigned int offset, size_t count)
> +{
> +       unsigned int bits;
> +       size_t remainder;

Add a newline here.

> +       /*
> +        * In case of multi-address chips that don't rollover reads to
> +        * the next slave address: truncate the count to the slave boundary,
> +        * so that the read never straddles slaves.
> +        */
> +       if (at24->chip.flags & AT24_FLAG_NO_RDROL) {
> +               bits = (at24->chip.flags & AT24_FLAG_ADDR16) ? 16 : 8;

There's no need for braces around the ternary operator's condition.

> +               remainder = BIT(bits) - offset;
> +               if (count > remainder)
> +                       count = remainder;
> +       }

Another newline here.

> +       if (count > io_limit)
> +               count = io_limit;
> +
> +       return count;
> +}
> +
>  static ssize_t at24_regmap_read(struct at24_data *at24, char *buf,
>                                 unsigned int offset, size_t count)
>  {
> @@ -289,9 +302,7 @@ static ssize_t at24_regmap_read(struct at24_data *at24, char *buf,
>         at24_client = at24_translate_offset(at24, &offset);
>         regmap = at24_client->regmap;
>         client = at24_client->client;
> -
> -       if (count > io_limit)
> -               count = io_limit;
> +       count = at24_adjust_read_count(at24, offset, count);
>
>         /* adjust offset for mac and serial read ops */
>         offset += at24->offset_adj;
> @@ -457,6 +468,8 @@ static void at24_get_pdata(struct device *dev, struct at24_platform_data *chip)
>
>         if (device_property_present(dev, "read-only"))
>                 chip->flags |= AT24_FLAG_READONLY;
> +       if (device_property_present(dev, "no-read-rollover"))
> +               chip->flags |= AT24_FLAG_NO_RDROL;
>
>         err = device_property_read_u32(dev, "size", &val);
>         if (!err)
> diff --git a/include/linux/platform_data/at24.h b/include/linux/platform_data/at24.h
> index 271a4e2..841bb28 100644
> --- a/include/linux/platform_data/at24.h
> +++ b/include/linux/platform_data/at24.h
> @@ -50,6 +50,8 @@ struct at24_platform_data {
>  #define AT24_FLAG_TAKE8ADDR    BIT(4)  /* take always 8 addresses (24c00) */
>  #define AT24_FLAG_SERIAL       BIT(3)  /* factory-programmed serial number */
>  #define AT24_FLAG_MAC          BIT(2)  /* factory-programmed mac address */
> +#define AT24_FLAG_NO_RDROL  BIT(1)     /* does not auto-rollover reads to */
> +                                       /* the next slave address */
>
>         void            (*setup)(struct nvmem_device *nvmem, void *context);
>         void            *context;
> --
> 1.9.1
>

Thanks,
Bartosz

Re: [PATCH v5 1/2] at24: support eeproms that do not auto-rollover reads.

[Uwe Kleine-König]

Hello,

On Thu, Dec 07, 2017 at 05:26:50PM +0100, Bartosz Golaszewski wrote:
> > +       if (at24->chip.flags & AT24_FLAG_NO_RDROL) {
> > +               bits = (at24->chip.flags & AT24_FLAG_ADDR16) ? 16 : 8;
> 
> There's no need for braces around the ternary operator's condition.

Even if not required, I'd keep them for clearity.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

Re: [PATCH v5 1/2] at24: support eeproms that do not auto-rollover reads.

[Bartosz Golaszewski]

2017-12-07 20:02 GMT+01:00 Uwe Kleine-König <u.kleine-koenig@pengutronix.de>:
> Hello,
>
> On Thu, Dec 07, 2017 at 05:26:50PM +0100, Bartosz Golaszewski wrote:
>> > +       if (at24->chip.flags & AT24_FLAG_NO_RDROL) {
>> > +               bits = (at24->chip.flags & AT24_FLAG_ADDR16) ? 16 : 8;
>>
>> There's no need for braces around the ternary operator's condition.
>
> Even if not required, I'd keep them for clearity.
>

I don't want to start bikeshedding, so I'll take it as it is, but I
prefer to avoid braces wherever it's not necessary.

Thanks,
Bartosz

Re: [PATCH v5 1/2] at24: support eeproms that do not auto-rollover reads.

[Uwe Kleine-König]

On Thu, Dec 07, 2017 at 10:33:51PM +0100, Bartosz Golaszewski wrote:
> 2017-12-07 20:02 GMT+01:00 Uwe Kleine-König <u.kleine-koenig@pengutronix.de>:
> > Hello,
> >
> > On Thu, Dec 07, 2017 at 05:26:50PM +0100, Bartosz Golaszewski wrote:
> >> > +       if (at24->chip.flags & AT24_FLAG_NO_RDROL) {
> >> > +               bits = (at24->chip.flags & AT24_FLAG_ADDR16) ? 16 : 8;
> >>
> >> There's no need for braces around the ternary operator's condition.
> >
> > Even if not required, I'd keep them for clearity.
> >
> 
> I don't want to start bikeshedding, so I'll take it as it is, but I
> prefer to avoid braces wherever it's not necessary.

For me the reasoning is: Most people (me included) don't know off-hand
if the semantic of

	a & b ? c : d

is
	(a & b) ? c : d

or

	a & (b ? c : d)

In some situations (e.g. a & b == c) gcc even warns when you don't add
syntactically needless parentheses. The case under discussion isn't such
an example though.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |