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From: Wolfram Sang <wsa@the-dreams.de>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>,
	dmaengine@vger.kernel.org,
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Subject: [RFC] dmaengine: rcar-dmac: set scatter/gather max segment size
Date: Fri, 14 Sep 2018 15:35:18 +0200	[thread overview]
Message-ID: <20180914133518.GA1413@kunai> (raw)

Hi Geert,

> > +       dmac->dev->dma_parms = &dmac->parms;
> > +       dma_set_max_seg_size(dmac->dev, 0x01000000);
> 
> That is one too much, cfr.
> 
>     drivers/dma/sh/rcar-dmac.c:#define RCAR_DMATCR_MASK             0x00ffffff

I see. Will fix and send an updated patch. Nice to see that I was not
totally wrong but just off-by-one.

> And yes, this depends on the data length, which is not known at probe time.
> Of course, dma_set_max_seg_size(dmac->dev, RCAR_DMATCR_MASK)
> should be safe, albeit (slightly) suboptimal.

True. But still *way* better than the current default of 64K.

Thanks for the heads up!

Regards,

   Wolfram

             reply	other threads:[~2018-09-14 13:35 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-14 13:35 Wolfram Sang [this message]
  -- strict thread matches above, loose matches on Subject: below --
2018-09-14 12:13 [RFC] dmaengine: rcar-dmac: set scatter/gather max segment size Geert Uytterhoeven
2018-09-13 14:52 Wolfram Sang

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