LKML Archive on lore.kernel.org
 help / color / Atom feed
From: "H. Nikolaus Schaller" <hns@goldelico.com>
To: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: Peter Ujfalusi <peter.ujfalusi@ti.com>,
	Tony Lindgren <tony@atomide.com>,
	Linux-OMAP <linux-omap@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Discussions about the Letux Kernel 
	<letux-kernel@openphoenux.org>
Subject: Re: [BISECTED, REGRESSION] OMAP3 onenand/DMA broken
Date: Fri, 3 Jan 2020 19:29:03 +0100
Message-ID: <521CC383-1118-480F-BC3B-B0E12F9F4CFC@goldelico.com> (raw)
In-Reply-To: <20200103172326.GF15023@darkstar.musicnaut.iki.fi>

Hi Aaro,

> Am 03.01.2020 um 18:23 schrieb Aaro Koskinen <aaro.koskinen@iki.fi>:
> 
> Hi,
> 
> On Fri, Jan 03, 2020 at 09:46:58AM +0100, H. Nikolaus Schaller wrote:
>>> Am 03.01.2020 um 09:17 schrieb Aaro Koskinen <aaro.koskinen@iki.fi>:
>>> When booting v5.4 (or v5.5-rc4) on N900, the console gets flooded with:
>>> 
>>> [    8.335754] omap2-onenand 1000000.onenand: timeout waiting for DMA
>>> [    8.365753] omap2-onenand 1000000.onenand: timeout waiting for DMA
>>> [    8.395751] omap2-onenand 1000000.onenand: timeout waiting for DMA
>>> [    8.425750] omap2-onenand 1000000.onenand: timeout waiting for DMA
>>> [    8.455749] omap2-onenand 1000000.onenand: timeout waiting for DMA
>>> [    8.485748] omap2-onenand 1000000.onenand: timeout waiting for DMA
>>> [    8.515777] omap2-onenand 1000000.onenand: timeout waiting for DMA
>>> [    8.545776] omap2-onenand 1000000.onenand: timeout waiting for DMA
>>> [    8.575775] omap2-onenand 1000000.onenand: timeout waiting for DMA
>>> 
>>> making the system unusable.
>> 
>> I can confirm that this issue exists but so far we failed to bisect
>> and make a proper report.
>> 
>> Sometimes the system boots fine and sometimes it fails.

Well, we boot from µSD and the number of the timeouts changes. So it may
be a race or depend on driver load sequence if we come to a login: or not.
But this is not the real bug.

>> 
>> It happens on omap3-gta04a5one.dts only, but not with omap3-gta04a4.dts
>> (both dm3730 but different NAND).
> 
> I tried three different boards (N810, N900 and N950) and it always
> fails reliably.

The big question is why the patch is harmful.

I tried to understand what the patch is doing (without any knowledge
about the DMA hard- or software architecture).

Basically it reorders error handling and some corner cases.
Maybe it handles one differently that happens only for OneNAND.

What did jump to my mind is that before the patch there is an
unconditional call to omap_dma_chan_read(c, CCR) if (!c->paused && c->running) 

And then DMA_COMPLETE is returned or ret if txstate == 0

With the new code the check for DMA_COMPLETE comes first and
directly leads to a return. Independently of txstate.

So if we have (!c->paused && c->running) and dma_cookie_status()
returns DMA_COMPLETE, there is no longer a call to omap_dma_chan_read()

Since I do not understand what omap_dma_chan_read() is doing,
and if (!c->paused && c->running) is relevant here,
I can not conclude if that is harmful.

But I can imagine that reading a register may have a side-effect of
resetting some bit like interrupt status registers.

I hope that Peter or Tony can respond soon.

BR and thanks,
Nikolaus




  reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-03  8:17 Aaro Koskinen
2020-01-03  8:46 ` H. Nikolaus Schaller
2020-01-03 17:23   ` Aaro Koskinen
2020-01-03 18:29     ` H. Nikolaus Schaller [this message]
2020-01-04  7:38 ` Peter Ujfalusi

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=521CC383-1118-480F-BC3B-B0E12F9F4CFC@goldelico.com \
    --to=hns@goldelico.com \
    --cc=aaro.koskinen@iki.fi \
    --cc=letux-kernel@openphoenux.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-omap@vger.kernel.org \
    --cc=peter.ujfalusi@ti.com \
    --cc=tony@atomide.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git