2016-01-05 19:58 GMT+01:00 Wolfram Sang <wsa@xxxxxxxxxxxxx>: > On Mon, Jan 04, 2016 at 03:01:54PM +0100, Bartosz Golaszewski wrote: >> 2016-01-02 21:50 GMT+01:00 Wolfram Sang <wsa@xxxxxxxxxxxxx>: >> > On Fri, Dec 11, 2015 at 02:55:10PM +0100, Bartosz Golaszewski wrote: >> >> 2015-12-11 13:08 GMT+01:00 Wolfram Sang <wsa@xxxxxxxxxxxxx>: >> >> > On Wed, Dec 02, 2015 at 11:25:17AM +0100, Bartosz Golaszewski wrote: >> >> >> Chips from the at24cs EEPROM series have an additional read-only memory area >> >> >> containing a factory pre-programmed serial number. In order to access it, a >> >> >> dummy write must be executed before reading the serial number bytes. >> >> > >> >> > Can't you instantiate a read-only EEPROM on this second address? Or a >> >> > seperate driver attaching to this address? What is the advantage of >> >> > having this in at24? >> >> > >> >> >> >> The regular memory area and serial number read-only block share the >> >> internal address pointer. We must ensure that there's no race >> >> conditions between normal EEPROM reads/writes and serial number reads. >> > >> > I don't get it. Both, regular at24 reads and the serial read, setup the >> > pointer every time by using two messages, first write to set the >> > pointer, then read. The per-adapter lock makes sure those two messages >> > will not get interrupted. >> >> If that's correct, then is there any need to have an additional mutex >> for at24_data? > > I can't see a need, yes. Then I'll see if it can be safely removed in the next iteration. >> In that case would the preferred method be to access the regular >> memory area like before - by allocating, for example, a 24c02 device - >> while allocating a second device - in that case 24cs02 - on the >> corresponding serial number address would give the user access to the >> serial number via the eeprom sysfs attribute (which for the latter >> would be read-only and 16 bytes in size)? > > Yes, a seperate driver for the second address is what I meant to suggest > in the above paragraph. Only that the data should probably be exported > via the NVMEM framework, not directly via sysfs. We have patches pending > doing that for at24. Right, but then these patches keep the driver backwards compatible in that they keep the 'eeprom' sysfs attribute, so it's still a viable option. > What happens if you assign another at24 instance (read-only) to the > second address? I mean, there is not only the serial number, but also a > MAC address IIRC. Nothing - it can't be read with the regular driver. Its protocol requires certain bits set just like in the function from patch 4/9 in this series. As for the MAC address - I can't find anything in the datasheet, and haven't heard about it. > Regards, > > Wolfram > Best regards, Bartosz Golaszewski -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
