From: Tony Lindgren <tony@atomide.com>
To: "Péter Ujfalusi" <peter.ujfalusi@ti.com>
Cc: linux-arm-kernel@lists.infradead.org,
Jarkko Nikula <jarkko.nikula@bitmer.com>,
linux-omap@vger.kernel.org
Subject: Re: Re: [PATCH 1/2] OMAP2+: DMA: Workaround for invalid source position
Date: Fri, 4 Nov 2011 13:08:26 -0700 [thread overview]
Message-ID: <20111104200826.GE31337@atomide.com> (raw)
In-Reply-To: <2603119.amz7RjSE3J@barack>
* Péter Ujfalusi <peter.ujfalusi@ti.com> [111104 02:00]:
> On Thursday 03 November 2011 14:27:56 Tony Lindgren wrote:
> >
> > Should these tests be done only after the errata re-read for both
> > src and dst patches? Otherwise the errata will not be handled?
>
> Yes that might be a good idea.
> I was trying to locate the original errata description for DMA_ERRATA_3_3, but
> it does not exist, or at least I can not find it. This only been mentioned in
> the kernel's comment.
Seems it got added with commit d3c9be2f.
> I'm not sure when this DMA_ERRATA_3_3 would have been in force. My guess would
> be that if someone wants to read the src/dst position right after the channel
> is disabled, but what would we expect it to return when the channel has been
> disabled?
No idea.. Or read it after stopping it?
> I mean what is the reasonable src/dst for a disabled channel? 0 is as good as
> any other number, probably the programmed start of the DMA transfer would be
> my best bet.
> I think the errata description for DMA_ERRATA_3_3 is not correct, and it is in
> fact to handle the case I'm also handling: Before the first DMA request the
> CDAC is 0 (since we configured it to be), the CSAC contains _something_ (most
> of the time 0, but can be random number).
> In some situation re-reading the src/dst position will give enough time to
> receive the first DMA request, which will update CDAC/CSAC registers.
Yeah could be since the handling is just an immediate re-read of the register..
> What do you think?
Probably the safest thing to do is move your check after the re-read test
in case there's more to the ERRATA_3_3.
Regards,
Tony
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WARNING: multiple messages have this Message-ID (diff)
From: tony@atomide.com (Tony Lindgren)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 1/2] OMAP2+: DMA: Workaround for invalid source position
Date: Fri, 4 Nov 2011 13:08:26 -0700 [thread overview]
Message-ID: <20111104200826.GE31337@atomide.com> (raw)
In-Reply-To: <2603119.amz7RjSE3J@barack>
* P?ter Ujfalusi <peter.ujfalusi@ti.com> [111104 02:00]:
> On Thursday 03 November 2011 14:27:56 Tony Lindgren wrote:
> >
> > Should these tests be done only after the errata re-read for both
> > src and dst patches? Otherwise the errata will not be handled?
>
> Yes that might be a good idea.
> I was trying to locate the original errata description for DMA_ERRATA_3_3, but
> it does not exist, or at least I can not find it. This only been mentioned in
> the kernel's comment.
Seems it got added with commit d3c9be2f.
> I'm not sure when this DMA_ERRATA_3_3 would have been in force. My guess would
> be that if someone wants to read the src/dst position right after the channel
> is disabled, but what would we expect it to return when the channel has been
> disabled?
No idea.. Or read it after stopping it?
> I mean what is the reasonable src/dst for a disabled channel? 0 is as good as
> any other number, probably the programmed start of the DMA transfer would be
> my best bet.
> I think the errata description for DMA_ERRATA_3_3 is not correct, and it is in
> fact to handle the case I'm also handling: Before the first DMA request the
> CDAC is 0 (since we configured it to be), the CSAC contains _something_ (most
> of the time 0, but can be random number).
> In some situation re-reading the src/dst position will give enough time to
> receive the first DMA request, which will update CDAC/CSAC registers.
Yeah could be since the handling is just an immediate re-read of the register..
> What do you think?
Probably the safest thing to do is move your check after the re-read test
in case there's more to the ERRATA_3_3.
Regards,
Tony
next prev parent reply other threads:[~2011-11-04 20:08 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-31 14:20 [PATCH 0/2] OMAP2+: DMA: fix src/dst position reporting Peter Ujfalusi
2011-10-31 14:20 ` [PATCH 1/2] OMAP2+: DMA: Workaround for invalid source position Peter Ujfalusi
2011-11-03 21:27 ` Tony Lindgren
2011-11-03 21:29 ` Tony Lindgren
2011-11-04 9:35 ` Péter Ujfalusi
2011-11-04 9:35 ` Péter Ujfalusi
2011-11-04 20:08 ` Tony Lindgren [this message]
2011-11-04 20:08 ` Tony Lindgren
2011-10-31 14:20 ` [PATCH 2/2] OMAP2+: DMA: Workaround for invalid destination position Peter Ujfalusi
2011-11-01 19:26 ` [PATCH 0/2] OMAP2+: DMA: fix src/dst position reporting Jarkko Nikula
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