Message-Id: <201508021108.52978@pali>
Date:	Sun, 2 Aug 2015 11:08:52 +0200
From:	Pali Rohár <pali.rohar@...il.com>
To:	Robert Hancock <hancockrwd@...il.com>
Cc:	Jeff Garzik <jeff@...zik.org>, Robert Hancock <hancockr@...w.ca>,
	Tejun Heo <tj@...nel.org>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	"linux-kernel" <linux-kernel@...r.kernel.org>
Subject: Re: linux: sata_nv: adma support

On Sunday 02 August 2015 03:45:32 Robert Hancock wrote:
> On Sat, Aug 1, 2015 at 2:09 PM, Pali Rohár <pali.rohar@...il.com>
> wrote:
> > On Thursday 25 December 2014 07:22:13 Robert Hancock wrote:
> >> On Tue, Dec 23, 2014 at 1:51 PM, Pali Rohár <pali.rohar@...il.com>
> >> 
> >> wrote:
> >> > Hello,
> >> > 
> >> > I have nvidia nforce4 motherboard with nvidia sata controller:
> >> > 
> >> > 00:07.0 IDE interface [0101]: NVIDIA Corporation CK804 Serial
> >> > ATA Controller [10de:0054] (rev f3)
> >> > 00:08.0 IDE interface [0101]: NVIDIA Corporation CK804 Serial
> >> > ATA Controller [10de:0055] (rev f3)
> >> > 
> >> > I manually enabled adma mode (which is disabled by default) by
> >> > adding sata_nv.adma=1 to grub cmdline. In git history I found
> >> > that enabling adma mode includes NCQ support and reduced CPU
> >> > overhead. It looks like adma mode is working, but at every boot
> >> > I see one same error message in dmesg:
> >> > 
> >> > [   16.823514] ata1.00: exception Emask 0x1 SAct 0x0 SErr 0x0
> >> > action 0x0
> >> > [   16.823520] ata1.00: CPB resp_flags 0x11: , CMD error
> >> > [   16.823524] ata1.00: failed command: SET FEATURES
> >> > [   16.823530] ata1.00: cmd ef/05:fe:00:00:00/00:00:00:00:00/40
> >> > tag 16
> >> > [   16.823530]          res 51/04:fe:00:00:00/00:00:00:00:00/40
> >> > Emask 0x1 (device error)
> >> > [   16.823533] ata1.00: status: { DRDY ERR }
> >> > [   16.823535] ata1.00: error: { ABRT }
> >> > 
> >> > When adma is disabled then this error message is not generated.
> >> 
> >> It looks like something is trying to issue a command to disable
> >> APM power management on the drive, and the command fails (likely
> >> because it doesn't support that command). I'm not sure where that
> >> would be coming from - I'm pretty sure the kernel doesn't issue
> >> that command itself. Something that's part of your distro
> >> perhaps?
> >> 
> >> I don't know why it would only be failing in ADMA mode either,
> >> though depending on where the command is coming from, maybe it's
> >> not being issued otherwise for some reason?
> >> 
> >> > What does that error message means? It is critical? What is that
> >> > command SET FEATURES doing? Are there any problems with adma
> >> > mode on nforce4 motherboards? Because I did not see any
> >> > problems (except that one error message).
> >> > 
> >> > --
> >> > Pali Rohár
> >> > pali.rohar@...il.com
> > 
> > Hello,
> > 
> > now after long time I did more investigation and that error is
> > reported for every connected HDD. I identified that it comes from
> > udev script
> > 
> >  /lib/udev/rules.d/85-hdparm.rules
> > 
> > which just call script /lib/udev/hdparm for every one connected
> > HDD.
> > 
> > Script /lib/udev/hdparm just call:
> >  /sbin/hdparm -B254 $DRIVE
> > 
> > And that -B254 cause above error message in dmesg log. Output from
> > 
> > hdparm is:
> >  /dev/sda:
> >   setting Advanced Power Management level to 0xfe (254)
> >   APM_level      = not supported
> > 
> > Any idea why in ADMA mode it cause above error (APM unsupported)
> > and in non ADMA mode it is working fine? Maybe APM ATA commands
> > should not be sent via ADMA?
> > 
> > Here is another output:
> >  $ sudo hdparm -I /dev/sda | grep -i power
> >  
> >             *    Power Management feature set
> >             
> >                  Power-Up In Standby feature set
> >             
> >             *    SET_FEATURES required to spinup after power up
> >             *    Host-initiated interface power management
> 
> The "set features" command is a non-data command so based on our
> current knowledge, it should work in ADMA mode. However, these NVIDIA
> SATAs are black boxes, and rather buggy ones at that, so it's
> possible there's an unknown issue there.
> 

Maybe I should note that hdparm -I did not generated any error message. 
I post is here because it show "Power Management feature set" is 
supported by HDD. This indicate that HDD supports -B (APM) command, 
right?

> The easiest way to test that would be to take out the condition check
> for qc->tf.protocol == ATA_PROT_NODATA in nv_adma_use_reg_mode in
> drivers/ata/sata_nv.c. That would force it to disable ADMA for all
> non-data commands.
> 

Ok, as now I have just SSH access to that machine, I will do kernel 
patching later (when I have physical access to it).

> I really don't know why Ubuntu is disabling APM on all drives on
> bootup however. Especially for laptops, that seems like a silly thing
> to do explicitly. Sounds like one of the silly things Ubuntu is known
> to do without consulting people.

Looks like this comes from upstream udev/systemd project :-( Anyway, for 
laptops on battery ubuntu has another set of scripts which turn on APM 
(based on connected/disconnected AC adapter).

That udev script which turn off APM is called when any disk is attached 
to system (so at boot time it is called for every one disk).

Now I just masked that udev script and it is no longer called...

Anyway if I call hdparm -B /dev/sda I get output:

APM_level      = not supported

And important is that there is no error message in dmesg. I get it only 
if I call hdparm -B with parameter (set option). But APM should be 
supported, right?

-- 
Pali Rohár
pali.rohar@...il.com

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