Hi Cyril,
On 09/10/2010 06:59 PM, Cyril Chemparathy wrote:
> Hi Mike,
>
> I have merged your latest two emails and responded to both here.
>
[...]
> One of the patches posted on my repo [1] replaces the dumb mdelay() with
> a bit more logic that calculates the worst-case access time. This
> mechanism may work a lot better for you. Would you mind trying it out?
>
You patch from [1] is working much more reliably now (well, 6 for 6 boot cycles as well as
several ifup/ifdown cycles). I do get the "resetting idled controlled" console message
every cycle, it seems that will be expected now.
[...]
>>
>> Also, your while(1) loops with the continue conditions on the second wait_for_user_access()
>> in the read and writes might need some consideration, i.e.:
>>
>> while (1) {
>> ret = wait_for_user_access(data);
>> if (ret == -EAGAIN)
>> continue;
>> if (ret < 0)
>> break;
>>
>> __raw_writel(reg, &data->regs->user[0].access);
>>
>> ret = wait_for_user_access(data);
>> if (ret == -EAGAIN)
>> continue;
>> ^^^^^^^^^ <--- this will re-issue the request.... what you want?
>
> Yes, the wait_for_user_access() would have reset the controller,
> throwing the current transaction out. The intent here is to restart the
> current transaction with a newly initialized controller.
>
OK. Makes sense. Looking at it felt like there was a chance for end endless spin, but that
seems unlikely given how that condition might fire.
[...]
>> Also, on the shutdown, I get a major kernel trace. Here is the dump, as much
>> as I could catch of it.... (I need a better terminal program)
>
> [...]
>> WARNING: at drivers/net/davinci_emac.c:1025 __cpdma_chan_free+0xac/0xb0()
>
> The current code spits out a huge volume of stuff as a result of a
> WARN_ON in the rx handler. The gitweb on [1] has a patch that fixes this.
>
Yes, these messages are no longer issued with the patches from [1]. Thanks.
> [...]
>>>> The MDIO module upgrade (rev 1.4 -> 1.5) could have something to do with
>>>> this behavior. Even so, I can't explain why this issue wasn't seen on
>>>> da8xx prior to this series. The original code should (at least in
>>>> theory) have sporadically locked up on emac open.
>>>>
>> I think, if I understand it correctly, that in the previous version of
>> this code, the emac was reset *prior* to enabling, scanning, and assigning
>> the associated phy on the MDIO bus. The new implementation sets up and scans
>> the MDIO bus first, then comes back around to the EMAC second... hits a reset,
>> and doesn't re-ENABLE the MDIO.
>
> AFAICS, that isn't entirely accurate. In the previous version, the mdio
> bus was being brought up at probe time in davinci_emac_probe(). The
> soft-reset was happening later on when the device is opened, in
> emac_hw_enable().
>
> The difference, however, is that the original code forced an
> emac_mii_reset() immediately after the emac_hw_enable(). This is not
> being done with the separated mdio, and that is the problem. In terms
> of behavior, with the current work around, the new and old versions
> should be close to identical. More below...
>
>> Also, maybe hitting the EMAC reset while the MDIO state machine is up is *bad*, I
>> seem to recall some text in the user's guide about waiting for the state
>> machine to stop before disabling it. I wonder if that also applies to reset?
>
> You are correct. EMAC soft-reset stops the MDIO mid-transaction, quite
> unlike disabling the module via the control register. Therefore, there
> is a risk that a badly designed phy could be left hanging in an
> arbitrary state. However, all earlier versions of the emac code have
> been exposed to this very same vulnerability (i.e. arbitrary emac
> soft-reset regardless of mdio state) all along.
>
Thanks for straightening me out on this, Cryil. Your patch series in [1] seems to
have resolved the issues I've been able to see on the da850 based board I'm using
here. I appreciate your patience and quick response. I may try to beat on it a
bit more with some network performance tests (even though it's not at all related
to the immediate problems you've fixed) -- we've had that on our list of todos
anyway for this module.
I think it would be good to float your patches over to davinci-next, if possible, before the
37 merge window opens... Speaking, of course, from a very partial perspective.
> [1]
> http://arago-project.org/git/people/?p=cyril/linux-tnetv107x.git;a=shortlog;h=refs/heads/emac-cpdma-mdio-fixes
-Mike
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