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? > So, it looks to me that it would be OK if a > serial read access gets inbetween a eeprom read access. Am I wrong? > 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)? 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
