at24: writing with SMBUS and no I2C_FUNC_SMBUS_WRITE_I2C_BLOCK

at24: writing with SMBUS and no I2C_FUNC_SMBUS_WRITE_I2C_BLOCK

[Curt Brune]

Hello -

I have a system that uses SMBUS, but without the
I2C_FUNC_SMBUS_WRITE_I2C_BLOCK functionality.  As it is today at24.c
will only support read-only mode for this case.

Looking at at24_eeprom_write() the comments indicate it only supports
page writes as the alternative is too slow.  This decision seems to be
the root of why SMBUS without I2C_FUNC_SMBUS_WRITE_I2C_BLOCK gives the
read-only situation.

The notion of "slow" seems a bit arbitrary to me.  Is there some other
technical reason or gotcha hiding here that you know of?

Would a nicely written patch that adds write support for this case be
acceptable?  I have not written it yet, but would like to.

Cheers,
Curt

Re: at24: writing with SMBUS and no I2C_FUNC_SMBUS_WRITE_I2C_BLOCK

[Wolfram Sang]

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> The notion of "slow" seems a bit arbitrary to me.  Is there some other
> technical reason or gotcha hiding here that you know of?

$ git show 7aeb96642f70139a194d685b132605836f6f8dbb

commit 7aeb96642f70139a194d685b132605836f6f8dbb
Author: Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>
Date:   Fri May 21 18:40:57 2010 +0200

    at24: Fall back to byte or word reads if needed
    
    Increase the portability of the at24 driver by letting it read from
    EEPROM chips connected to cheap SMBus controllers that support neither
    raw I2C messages nor even I2C block reads. All SMBus controllers
    should support either word reads or byte reads, so read support
    becomes universal, much like with the legacy "eeprom" driver.
    
    Obviously, this only works with EEPROM chips up to AT24C16, that use
    8-bit offset addressing. 16-bit offset addressing is almost impossible
    to support on SMBus controllers.
    
    I did not add universal support for writes, as I had no immediate need
    for this, but it could be added later if needed (with the same
    performance issue as byte and word reads have, of course.)
    
    Signed-off-by: Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>
    Reviewed-by: Wolfram Sang <w.sang-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
    Cc: Konstantin Lazarev <klazarev-rphTv4pjVZMJGwgDXS7ZQA@public.gmane.org>

> Would a nicely written patch that adds write support for this case be
> acceptable?  I have not written it yet, but would like to.

Yes, it would.

All the best,

   Wolfram


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