From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tony Lindgren Subject: Re: [PATCH 15/15] tty: serial: 8250: omap: add dma support Date: Thu, 21 Aug 2014 11:44:16 -0700 Message-ID: <20140821184416.GF10066@atomide.com> References: <1408124563-31541-1-git-send-email-bigeasy@linutronix.de> <1408124563-31541-16-git-send-email-bigeasy@linutronix.de> <20140815210211.GD9239@atomide.com> <53F5AF0D.5060409@linutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <53F5AF0D.5060409@linutronix.de> Sender: linux-serial-owner@vger.kernel.org To: Sebastian Andrzej Siewior Cc: linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org, balbi@ti.com, Vinod Koul , Greg Kroah-Hartman List-Id: linux-omap@vger.kernel.org * Sebastian Andrzej Siewior [140821 01:37]: > On 08/15/2014 11:02 PM, Tony Lindgren wrote: > > * Sebastian Andrzej Siewior [140815 11:13]: > >> +#ifdef CONFIG_SERIAL_8250_DMA > >> + if (pdev->dev.of_node) { > >> + /* > >> + * Oh DMA support. If there are no DMA properties in the DT then > >> + * we will fall back to a generic DMA channel which does not > >> + * really work here. To ensure that we do not get a generic DMA > >> + * channel assigned, we have the the_no_dma_filter_fn() here. > >> + * To avoid "failed to request DMA" messages we check for DMA > >> + * properties in DT. > >> + */ > >> + ret = of_property_count_strings(pdev->dev.of_node, "dma-names"); > >> + if (ret == 2) { > >> + up.dma = &priv->omap8250_dma; > >> + priv->omap8250_dma.fn = the_no_dma_filter_fn; > >> + priv->omap8250_dma.rx_size = RX_TRIGGER; > >> + priv->omap8250_dma.rxconf.src_maxburst = RX_TRIGGER; > >> + priv->omap8250_dma.txconf.dst_maxburst = TX_TRIGGER; > >> + > >> + if (of_machine_is_compatible("ti,am33xx")) > >> + up.bugs |= UART_BUG_DMATX; > >> + } > >> + } > >> +#endif > > > > Hmm I wonder if there's a more generic solution to this? > > To what exactly? The trigger level, the TX-bug or using DMA in the > first place? Oh sorry, I meant to having to do of_property_count_strings to figure out if it's correct or not. > > It would be also nice to be able to specify the use of DMA from > > the board specific .dts file. > > Really? I don't see this requirement for MMC for instance. However you > still could provide an empty "dma-names" property in your board .dts > file if you do not want use DMA. Would this work? OK yeah that works. And that's needed mostly because of the issue below. > > Also, with DMA enabled, looks like omap deeper idle states are > > blocked as the DMA stays reserved. After I commented out the > > DMA info for my console UART, PM started working. > > Hmm. This would explain something. This would mean that I should cancel > the RX DMA transfer in the PM-suspend routine. Let me see how that > works. OK and if the DMA works with PM, then I don't see why we would not want to have it automatically enabled. BTW, looks like the ports move around now though. If set a port to disabled with status = "disabled"; in the .dts file, you'll get a different console which does not happen with omap-serial I believe. Regards, Tony