[PATCH] i2c-EEPROM: Export memory accessor

[PATCH] i2c-EEPROM: Export memory accessor

[Pantelis Antoniou]

Various platforms need access to the EEPROM in other
places besides their platform registration callbacks.
Export the memory accessor to the i2c_client and implement
it for the at24 driver.

And before you ask, no, the platform callback can't be used
for anything that depends on DT.

Signed-off-by: Pantelis Antoniou <panto@antoniou-consulting.com>
---
 drivers/misc/eeprom/at24.c |  5 +++++
 include/linux/i2c.h        | 24 ++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index ab1ad41..4f88ae65 100644
--- a/drivers/misc/eeprom/at24.c
+++ b/drivers/misc/eeprom/at24.c
@@ -609,6 +609,9 @@ static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
 
 	at24->client[0] = client;
 
+	/* export accessor */
+	client->macc = &at24->macc;
+
 	/* use dummy devices for multiple-address chips */
 	for (i = 1; i < num_addresses; i++) {
 		at24->client[i] = i2c_new_dummy(client->adapter,
@@ -619,6 +622,7 @@ static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
 			err = -EADDRINUSE;
 			goto err_clients;
 		}
+		at24->client[i]->macc = &at24->macc;
 	}
 
 	err = sysfs_create_bin_file(&client->dev.kobj, &at24->bin);
@@ -637,6 +641,7 @@ static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
 			   I2C_SMBUS_WORD_DATA ? "word" : "byte");
 	}
 
+
 	/* export data to kernel code */
 	if (chip.setup)
 		chip.setup(&at24->macc, chip.context);
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 800de22..e20ad4e 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -33,6 +33,7 @@
 #include <linux/of.h>		/* for struct device_node */
 #include <linux/swab.h>		/* for swab16 */
 #include <uapi/linux/i2c.h>
+#include <linux/memory.h>
 
 extern struct bus_type i2c_bus_type;
 extern struct device_type i2c_adapter_type;
@@ -229,9 +230,32 @@ struct i2c_client {
 	struct device dev;		/* the device structure		*/
 	int irq;			/* irq issued by device		*/
 	struct list_head detected;
+
+	/* export accessor */
+	struct memory_accessor *macc;
 };
 #define to_i2c_client(d) container_of(d, struct i2c_client, dev)
 
+static inline ssize_t i2c_memory_read(struct i2c_client *client, char *buf, off_t offset,
+		size_t count)
+{
+	struct memory_accessor *macc = client->macc;
+
+	if (macc == NULL || macc->read == NULL)
+		return -ENODEV;
+	return (*client->macc->read)(macc, buf, offset, count);
+}
+
+static inline ssize_t i2c_memory_write(struct i2c_client *client, const char *buf, off_t offset,
+		size_t count)
+{
+	struct memory_accessor *macc = client->macc;
+
+	if (macc == NULL || macc->write == NULL)
+		return -ENODEV;
+	return (*client->macc->write)(macc, buf, offset, count);
+}
+
 extern struct i2c_client *i2c_verify_client(struct device *dev);
 extern struct i2c_adapter *i2c_verify_adapter(struct device *dev);
 
-- 
1.7.12

Re: [PATCH] i2c-EEPROM: Export memory accessor

[David Daney]

On 10/31/2012 08:56 AM, Pantelis Antoniou wrote:
> Various platforms need access to the EEPROM in other
> places besides their platform registration callbacks.
> Export the memory accessor to the i2c_client

i2c_clients are *not* intrinsically memory, so adding this to the 
generic i2c_client structure doesn't really make sense.   What would the 
semantics of this interface be with respect to temperature sensors and 
GPIO expanders?

NACK.


> and implement
> it for the at24 driver.
>
> And before you ask, no, the platform callback can't be used
> for anything that depends on DT.

Why can't you just allocate (and populate) a struct at24_platform_data 
for the device if it isn't supplied by whatever created the device?

Re: [PATCH] i2c-EEPROM: Export memory accessor

[Pantelis Antoniou]

Hi David,

On Oct 30, 2012, at 8:46 PM, David Daney wrote:

> On 10/31/2012 08:56 AM, Pantelis Antoniou wrote:
>> Various platforms need access to the EEPROM in other
>> places besides their platform registration callbacks.
>> Export the memory accessor to the i2c_client
> 
> i2c_clients are *not* intrinsically memory, so adding this to the generic i2c_client structure doesn't really make sense.   What would the semantics of this interface be with respect to temperature sensors and GPIO expanders?
> 
> NACK.
> 

It's only filled in for EEPROM devices. There's no other I2C memory read interface for kernel clients.

> 
>> and implement
>> it for the at24 driver.
>> 
>> And before you ask, no, the platform callback can't be used
>> for anything that depends on DT.
> 
> Why can't you just allocate (and populate) a struct at24_platform_data for the device if it isn't supplied by whatever created the device?
> 
> 
> 

There are no platform_data in the case of device tree only generic-boards. Everything is configured via the DT and there are
no callbacks. DT is a purely data driver concept.

I'm open to suggestions on how to read an EEPROM from another kernel client, when there's no such thing as platform_data anymore.

Regards

-- Pantelis

Re: [PATCH] i2c-EEPROM: Export memory accessor

[David Daney]

On 10/30/2012 11:51 AM, Pantelis Antoniou wrote:
> Hi David,
>
> On Oct 30, 2012, at 8:46 PM, David Daney wrote:
>
>> On 10/31/2012 08:56 AM, Pantelis Antoniou wrote:
>>> Various platforms need access to the EEPROM in other
>>> places besides their platform registration callbacks.
>>> Export the memory accessor to the i2c_client
>>
>> i2c_clients are *not* intrinsically memory, so adding this to the generic i2c_client structure doesn't really make sense.   What would the semantics of this interface be with respect to temperature sensors and GPIO expanders?
>>
>> NACK.
>>
>
> It's only filled in for EEPROM devices. There's no other I2C memory read interface for kernel clients.


Basically you are tacking on a registery of memory devices to some 
random data structure that has nothing to do with memory.

Instead ...

>
>>
>>> and implement
>>> it for the at24 driver.
>>>
>>> And before you ask, no, the platform callback can't be used
>>> for anything that depends on DT.
>>
>> Why can't you just allocate (and populate) a struct at24_platform_data for the device if it isn't supplied by whatever created the device?
>>
>>
>>
>
> There are no platform_data in the case of device tree only generic-boards. Everything is configured via the DT and there are
> no callbacks. DT is a purely data driver concept.
>
> I'm open to suggestions on how to read an EEPROM from another kernel client, when there's no such thing as platform_data anymore.
>

... you need some sort of collection memory devices that can be queried 
by phandle and/or some other handle.

Any device that implements the struct memory_accessor interface could 
add itself to the collection, then code that needs to use the 
memory_accessor interface would look up the proper target for the 
operation by phandle or whatever other handle the system is using.

Similar to how of_phy_find_device() works.

I don't know if it would be possible to create a 'memory_accessor' bus, 
but that is one idea I had.

David Daney


> Regards
>
> -- Pantelis
>
>
>
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