From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Peter Ujfalusi <peter.ujfalusi@ti.com>,
devicetree@vger.kernel.org, jsarha@ti.com,
dri-devel@lists.freedesktop.org
Subject: Re: [PATCH v2 2/2] drm/omap: partial workaround for DRA7xx DMM errata i878
Date: Wed, 04 Apr 2018 14:08:52 +0300 [thread overview]
Message-ID: <7256187.xpsYJETdA1@avalon> (raw)
In-Reply-To: <1ffef122-18d8-fc85-afff-02c8ca3bb0ca@ti.com>
Hi Tomi,
On Wednesday, 4 April 2018 13:50:43 EEST Tomi Valkeinen wrote:
> On 04/04/18 00:11, Laurent Pinchart wrote:
> >> + dma_async_issue_pending(dmm->wa_dma_chan);
> >> + status = dma_sync_wait(dmm->wa_dma_chan, cookie);
> >
> > dma_sync_wait() has a 5s timeout. You're calling this function with a
> > spinlock held. The end result might be slightly better than a complete
> > system lock as caused by the bug described in i878, but only slightly.
>
> When does the timeout trigger? I presume it only happens when things are
> badly broken on the HW or driver level, and when things work normally,
> the wait is very short.
It shouldn't happen when things go right, and I indeed expect the transfer to
complete quite fast. I would however like to get real numbers there, we should
measure how long the transfer typically takes.
> > Unless I'm mistaken the reason you can't sleep here is because of the need
> > to access registers in the interrupt handler. Could we use threaded IRQs
> > to solve this ?
>
> Yes, I think that's the reason. Probably we could use threaded IRQs.
>
> Also, I'm not sure if this is a big issue. If the dma_sync_wait
> timeouts, things are already rather broken. Then again, any wait in an
> irq context is not that nice. But if the wait is just a few loops long,
> it's not really even a wait...
--
Regards,
Laurent Pinchart
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next prev parent reply other threads:[~2018-04-04 11:08 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-22 13:42 [PATCH v2 0/2] drm/omap: Workaround for errata i878 Peter Ujfalusi
2018-03-22 13:42 ` [PATCH v2 1/2] dt-bindings: arm: omap: dmm: Document new compatible for DRA7xx family Peter Ujfalusi
2018-03-23 8:31 ` Peter Ujfalusi
2018-04-03 20:48 ` Laurent Pinchart
2018-03-26 22:24 ` Rob Herring
2018-04-03 20:44 ` Laurent Pinchart
2018-03-22 13:42 ` [PATCH v2 2/2] drm/omap: partial workaround for DRA7xx DMM errata i878 Peter Ujfalusi
2018-03-23 8:32 ` Peter Ujfalusi
2018-03-29 10:18 ` Tomi Valkeinen
2018-03-29 12:11 ` Peter Ujfalusi
2018-04-03 21:11 ` Laurent Pinchart
2018-04-04 7:37 ` Tomi Valkeinen
2018-04-04 9:51 ` Laurent Pinchart
2018-04-04 10:02 ` Tomi Valkeinen
2018-04-04 10:28 ` Laurent Pinchart
2018-04-04 10:33 ` Tomi Valkeinen
2018-04-04 11:17 ` Laurent Pinchart
2018-04-04 10:50 ` Tomi Valkeinen
2018-04-04 11:08 ` Laurent Pinchart [this message]
2018-04-10 6:50 ` Peter Ujfalusi
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