Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752421AbbFDGnK (ORCPT ); Thu, 4 Jun 2015 02:43:10 -0400 Received: from mail-oi0-f45.google.com ([209.85.218.45]:36332 "EHLO mail-oi0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752081AbbFDGnA (ORCPT ); Thu, 4 Jun 2015 02:43:00 -0400 MIME-Version: 1.0 In-Reply-To: <8fc4b9f5291a509c4c35782a1337bf536f1019af.1433364398.git.hramrach@gmail.com> References: <8fc4b9f5291a509c4c35782a1337bf536f1019af.1433364398.git.hramrach@gmail.com> Date: Thu, 4 Jun 2015 08:42:59 +0200 X-Google-Sender-Auth: CLHUHuw-Tz7e12wO-n9FcZaypO0 Message-ID: Subject: Re: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size. From: Geert Uytterhoeven To: Michal Suchanek Cc: Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , Russell King , Kukjin Kim , Krzysztof Kozlowski , Vinod Koul , Dan Williams , David Woodhouse , Brian Norris , Han Xu , Mark Brown , Geert Uytterhoeven , Marek Vasut , =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= , Alison Chaiken , Huang Shijie , Ben Hutchings , Knut Wohlrab , =?UTF-8?B?QmVhbiBIdW8g6ZyN5paM5paMIChiZWFuaHVvKQ==?= , "grmoore@altera.com" , "devicetree@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-samsung-soc@vger.kernel.org" , dmaengine@vger.kernel.org, MTD Maling List , linux-spi Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2783 Lines: 65 On Wed, Jun 3, 2015 at 11:26 PM, Michal Suchanek wrote: > On sunxi the SPI controller currently does not have DMA support and fails > any transfer larger than 63 bytes. This is a driver limitation, not a hardware limitation. > On Exynos the pl330 DMA controller fails any transfer larger than 64kb > when using slower speed like 40MHz and any transfer larger than 128bytes > when running at 133MHz. This may be a driver bug. > The best thing is that in both cases the controller can just lock up and > never finish potentially leaving the hardware in unusable state. > > So it is required that the m25p80 driver actively prevents doing > transfers that are too large for the current driver state on a > particular piece of hardware. OK. > Signed-off-by: Michal Suchanek > > -- > > Update commit message and documentation text. > --- > .../devicetree/bindings/mtd/jedec,spi-nor.txt | 6 ++++++ > drivers/mtd/devices/m25p80.c | 24 ++++++++++++++++++++-- > 2 files changed, 28 insertions(+), 2 deletions(-) > > diff --git a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt > index 2bee681..4e63ae8 100644 > --- a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt > +++ b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt > @@ -19,6 +19,12 @@ Optional properties: > all chips and support for it can not be detected at runtime. > Refer to your chips' datasheet to check if this is supported > by your chip. > +- linux,max_tx_len : With some SPI controller drivers possible transfer size is > + limited. This may be hardware or driver bug. > + Transfer data in chunks no larger than this value. > + Using this option may severely degrade performance and > + possibly flash memory life when max_tx_len is smaller than > + flash page size (typically 256 bytes) DT describes the hardware, not buggy drivers. So IMHO this doesn't belong in DT, but it can be a field in struct spi_master. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/