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Message-ID: <20140917084120.GA6369@Robin-OptiPlex-780> Date: Wed, 17 Sep 2014 16:41:22 +0800 From: Robin Gong <b38343@...escale.com> To: Lucas Stach <l.stach@...gutronix.de> CC: <mark.rutland@....com>, <devicetree@...r.kernel.org>, <linux@....linux.org.uk>, <pawel.moll@....com>, <ijc+devicetree@...lion.org.uk>, <linux-kernel@...r.kernel.org>, <robh+dt@...nel.org>, <linux-arm-kernel@...ts.infradead.org>, <kernel@...gutronix.de>, <galak@...eaurora.org>, <shawn.guo@...escale.com> Subject: Re: [PATCH v2] ARM: dts: imx6dl: disable dma support for spi on i.mx6dl On Tue, Sep 16, 2014 at 11:50:06AM +0200, Lucas Stach wrote: > Hi Robin, > > Am Dienstag, den 16.09.2014, 11:41 +0800 schrieb Robin Gong: > > Hi Lucas, > > I understood your concern,but looks we have to break old DT. > > Sorry, but this isn't going to happen. And honestly I don't even see the > need to do so. > > > Our old DT > > support SPI DMA on i.mx6q/dl(v2,b3810c3dc1bcbc6a), but the DMA support patch > > for SPI driver is still in reviewing(v6). > > So this means now is the time to fix this driver patch to not enable DMA > on imx6dl. Nobody will experience any breakage in this case. > Sorry, i.mx6q and i.mx6dl are totally same, not only IP but also clock. So we can't distinguish them except for different compatible name.... > > So the violation you mentioned comes > > if someone use the DT during the time(from v2 to spi driver patch upstreamed). > > The different behaviors on different chips(only i.mxdl can't pass strength > > test) are just found from last month, this is why I sent the patch for disable > > SPI DMA support on i.mx6dl during I sent v6 patch for spi driver. I think that's > > make sense, because DTs are also in development, new difference between different > > chips maybe found in the future although they share the same IP.... > > Yes, I can check cpu type by looking at DT in spi driver, but it's not nice. > > Yeah it would have been nicer if we had an explicit DT compatible for > the imx6dl ecspi version, but it's not there, so we have to cope with > this. > > > So I'm afraid that we have to break the old DTs in the gap between the two > > levels patch accepted cycle. > > > > On Mon, Sep 15, 2014 at 11:41:13AM +0200, Lucas Stach wrote: > > > Am Mittwoch, den 10.09.2014, 13:30 +0800 schrieb Robin Gong: > > > > There is one weird data in rxfifo after one full rx/tx transfer > > > > done sometimes. It looks a design issue and hard to workaround > > > > totally, so disable dma functhion here. And will re-enable it > > > > once the root cause found. > > > > > > > Sorry, I'm late to this as Shawn seems to already have picked up this > > > patch, but this isn't the right way to fix the problem. > > > > > > We made it clear at kernel summit last year that we try to not break > > > existing DTs as booting a new kernel with an old DT is a valid use case. > > > While you don't strictly violate this rule what you do here is only > > > fixing systems booting with a new DT while leaving others broken. > > > > > > If you are working around a hardware problem please disable DMA support > > > in the driver. This will also allow you to enable it again, if you find > > > another workaround without touching the DT again. > > > > > > So this patch gets a NAK from me. > > > > > Regards, > Lucas > -- > Pengutronix e.K. | Lucas Stach | > Industrial Linux Solutions | http://www.pengutronix.de/ | > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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