Messages in this thread | | | Date | Wed, 18 Mar 2015 20:24:18 -0700 | From | Guenter Roeck <> | Subject | Re: [PATCH] eeprom: at24: Add support for large EEPROMs connected to SMBus adapters |
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On 03/18/2015 06:27 AM, Wolfram Sang wrote: > On Mon, Mar 16, 2015 at 09:20:49PM -0700, Guenter Roeck wrote: >> On Mon, Feb 16, 2015 at 01:09:51PM +0100, Wolfram Sang wrote: >>> Hi Guenter, >>> >>>> I wonder where we are with thisp patch; I don't recall a reply to my previous >>>> e-mail. >>> >>> Sorry for the late reply. I needed to recover from a HDD headcrash :( >>> >>>> Do you need some more time to think about it ? Otherwise I'll publish an >>>> out-of-tree version of the at24 driver with the patch applied on github, >>>> for those who might need the functionality provided by this patch. >>> >>> Your last mail made me aware of why we were missing each other before. I >>> see your point now, but yes, still need to think about it. My plan is to >>> have a decision until the 3.21 merge window. >>> >> Hi Wolfram, >> >> any news ? > > Yes :) > > The main misunderstanding we had before was: You were talking about > multi-master safety between transfers, while I was thinking about > multi-master safety between messages. While we need to guarantee this > for the latter, you are right about the former, sadly. True multi-master > safety between transfers is probably like a can of worms currently. > > Still, I think we have a race with your patch when having two read > processes. If b) kicks in after a) has just set the eeprom pointer, a) > will not read the data it wants. For that to prevent, we should take the > adapter_lock during those two transfers needed for the read you > implemented. My preferred solution would be to have __smbus_transfer > like we have __i2c_transfer and then using that. Some mux code could > also make use out of that. But if you are going to use > adapter->algo->smbus_xfer() directly, well, then be it. >
You are right, that is a problem. Not for eeprom access itself - that already has a mutex - but for parallel access to the chip through the eeprom file and, say, by i2cdump.
I don't call that multi-master, though, so I guess we may have a bit of a terminology problem.
I'll see what I can come up with, but I am not sure if I'll find the time before the 4.1 commit window opens. Company has a working solution (kind of), so now I'll have to do this on my own time ;-).
Thanks, Guenter
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