On Dec 02, Corey Ashford wrote:
I just got a new system with precisely that board B450 and after running sensors-detect I was lead to this thread. Is it safe to try your out-of-tree module on this board of will it simply not work? I can provide extensive testing for what it's worth. R.On Mon, Dec 2, 2019 at 3:09 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:On Mon, Dec 02, 2019 at 02:33:27PM -0800, Corey Ashford wrote: > On Mon, Dec 2, 2019 at 9:52 AM Guenter Roeck <linux@xxxxxxxxxxxx> wrote: > > > > On Mon, Dec 02, 2019 at 09:07:10AM -0800, Corey Ashford wrote: > > > On Mon, Dec 2, 2019 at 6:32 AM Guenter Roeck <linux@xxxxxxxxxxxx> wrote: > > > > > > > > On 11/29/19 8:48 PM, Corey Ashford wrote: > > > > > On Fri, Nov 29, 2019 at 8:17 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote: > > > > >> > > > > >> On 11/29/19 6:11 PM, Corey Ashford wrote: > > > > >>> Hello folks. I am running a newly-built system that uses an IT8686E > > > > >>> chip. Currently, the latest kernel from kernel.org doesn't have code > > > > >>> in drivers/hwmon/it87.c to support it, however, I found some source on > > > > >>> the net which has added support for quite a few more variants of that > > > > >>> brand of Super I/O chip: > > > > >>> https://github.com/xdarklight/hwmon-it87/blob/master/it87.c > > > > >>> I tried it out by building the module and "insmod"ing it into my > > > > >>> running system, and it appears to work fine. > > > > >>> > > > > >>> It seems the original developer had a difficult time pushing the > > > > >>> changes upstream, so he abandoned the project. > > > > >>> > > > > >> > > > > >> I abandoned the project (and dropped the driver from my github page) > > > > >> because people started _demanding_ that I push the driver from github > > > > >> upstream, without offering any assistance whatsoever. > > > > >> > > > > >>> My thought was that I could add support for just the IT8686E chip as a > > > > >>> single patch, and since I can test it locally I would have a better > > > > >>> chance of getting the patch accepted. The changes to the source at > > > > >>> the above git tree have quite a number of changes that aren't really > > > > >>> necessary for supporting the IT8686E chip, so I think the patch could > > > > >>> be pretty small, but will still credit the original author. > > > > >>> > > > > >> > > > > >> IT8686 is a multi-page chip, meaning you'll need the entire protection > > > > >> against multi-page accesses by the EC in the system. It also supports > > > > >> the new temperature map. I don't think it is that simple. > > > > >> > > > > >> Guenter > > > > > > > > > > Thanks for the quick reply! > > > > > > > > > > When you said they didn't offer any assistance, do you mean assistance > > > > > with testing? If so, how about if the support is trimmed out for the > > > > > newly-added chips that have no available test system volunteers, and > > > > > then slowly add those back as people make test systems and testing > > > > > time available. Should I presume that you have access to one or more > > > > > systems with the added ITnnnn chips? I volunteer my system for > > > > > testing the IT8686E support. > > > > > > > > > > > > > Testing and, more importantly, detailed code review. No one but me has > > > > seriously (if at all) scrutinized that code for years. Just picking it > > > > into mainline and hope that it won't cause trouble is, by itself, troublesome. > > > > > > > > On top of that, the multi-page access problems are well known by board vendors > > > > using this chip as well as by the chip vendor. Yet, neither board vendors nor > > > > ITE talk with kernel developers. The workarounds I implemented are based on > > > > information I got from one of the Windows tools developers, and are not > > > > validated by any board vendor nor by ITE. Every board vendor I tried to contact > > > > tells me that they don't support Linux, and I never got any reply from ITE. > > > > I do know that the code causes problems on early Gigabyte board using the 8686 > > > > and similar multi-page chips. Just accessing the chip from Linux may cause trouble > > > > because the built-in EC tries to access it as well in parallel (I suspect this > > > > causes the board to reset because that access is turned off for a while by > > > > the driver). This is all fine for an out-of-tree driver, but it would be > > > > unacceptable in the upstream kernel. > > > > > > > > In summary, you'll not only need to port the code, you'll also need to establish > > > > contact to ITE and/or to board vendors to ensure that the code works as intended > > > > with the EC on the affected boards. > > > > > > > > Guenter > > > > > > Ah, thank you for your detailed explanation. How you did as much as > > > you did is beyond me. ITE's web site seems to lack any usable > > > information, and doesn't even list the IT8686 as one of their chips. > > > Other "supported" chips don't appear to have any documentation easily > > > available, other than a very generic-y description of the chip. Quite > > > an uphill battle for marginal gain. > > > > > Exactly. The only real recommendation I have at this time is for anyone > > running Linux to stay away from boards with ITE chips. > > > > > Is it possible there's a way to access the sensors by using the EC as > > > a proxy, rather than trying to gain direct and exclusive access to the > > > sensors? Just a thought. I have no idea of the architecture of these > > > things. Your mention of EC was the first I had heard of it :/ > > > > > > > Not that I know of, sorry. The EC is actually running inside the Super-IO > > chip(s). I have no idea if and how it is accessible from Linux. Either case, > > that would be even worse, since EC programming is board vendor specific. > > > > Guenter > > Just for my clarification, it seems that what you're implying is that > the embedded EC still uses the SMbus to access those paged registers, > and so needs to use the same mechanism that an external device would > use. If that's true, ugh. If it has its own private access to the > entire register set in one "address space", it could bypass the paging > mechanism. > There are typically two Super-IO chips on those boards. For example, Gigabyte B450 AORUS M has an IT8792 and an IT8686. The EC on one chip accesses the other chip through the I2C interface. Or at least that is what I think is happening... hard to be sure without board/chip vendor support.
Some of the recent chips solve the problem by memory mapping the entire register space (unpaged) into memory. This way the Linux driver (and the Windows driver) can access chip registers directly without having to select a page. That isn't supported on the 8686, unfortunately.Ah, that makes sense now. So I guess what's worse is that now you have a combination of two chips, which are not necessarily always paired with each other (e.g. IT8792->IT8686 vs. IT8795 [made up #]->IT8686). I give up :) At least the out-of-tree driver source has been working nicely for my machine for a couple of weeks, with no observed glitches, resets, etc. I'm happy. Thanks for the discussion of this little backwater area of the kernel :) - Corey
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