From mboxrd@z Thu Jan 1 00:00:00 1970 From: computersforpeace@gmail.com (Brian Norris) Date: Fri, 6 Feb 2015 00:33:45 -0800 Subject: [PATCH v2 1/2] mtd: nand: pxa3xx: Fix PIO FIFO draining In-Reply-To: <20150206091307.1162b123@bbrezillon> References: <1422284164-16867-1-git-send-email-maxime.ripard@free-electrons.com> <1422284164-16867-2-git-send-email-maxime.ripard@free-electrons.com> <20150204111028.2f0bd376@bbrezillon> <20150206010835.GB30781@ld-irv-0074> <20150206091307.1162b123@bbrezillon> Message-ID: <20150206083345.GE4434@norris-Latitude-E6410> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Fri, Feb 06, 2015 at 09:13:07AM +0100, Boris Brezillon wrote: > Hi Brian, > > On Thu, 5 Feb 2015 17:08:35 -0800 > Brian Norris wrote: > > On Wed, Feb 04, 2015 at 11:10:28AM +0100, Boris Brezillon wrote: > > > On Mon, 26 Jan 2015 15:56:03 +0100 > > > Maxime Ripard wrote: > > > > + /* > > > > + * According to the datasheet, when reading > > > > + * from NDDB with BCH enabled, after each 32 > > > > + * bits reads, we have to make sure that the > > > > + * NDSR.RDDREQ bit is set > > > > + */ > > > > > > I know the datasheet says this bit should be checked after each > > > transfer, but I wonder if we shouldn't check it before reading the data. > > > What happens if you drain all the data available in the FIFO ? Is the > > > controller still setting the RDDREQ bit ? > > > > > > Moreover, the datasheet says this RDDREQ bit should be checked after > > > each 32 bytes (not 32 bits) transfer. > > > Testing it after each readl call shouldn't hurt though. > > > > Seems like that could quite possibly kill performance unnecessarily, > > couldn't it? But then, PIO is probably not that fast in the first > > place... > > Absolutety, my point was, it shouldn't hurt from a functional POV, but > yes it will definitely impact performances. OK. > But that's not the first thing I would rework of if you're concerned > about performances: when doing PIO read/write, the page read/write > operations (I mean the part reading the internal fifo) are all done in > interrupt context (called from pxa3xx_nand_irq), and doing this will > prevent any other interrupt from taking place while you are > draining/filling the FIFO :-(. ...which reminds me; the jiffies-based timeout in this patch isn't going to work in interrupt context. So it needs to be replaced either with a tight udelay() loop, or it needs to be moved out of the ISR. > An alternative would be to move this part into the read/write_buf > functions, but that's a lot of work... Yeah, that probably would be preferable, but I suppose it's not urgent either. Brian