From mboxrd@z Thu Jan 1 00:00:00 1970 From: s.hauer@pengutronix.de (Sascha Hauer) Date: Thu, 24 Jun 2010 09:27:32 +0200 Subject: [PATCHv3 4/5] mtd: mxc_nand fixups In-Reply-To: <80lja6awlb.fsf@merkur.tec.linutronix.de> References: <20100618205401.GA12115@pengutronix.de> <80sk4ivkga.fsf@merkur.tec.linutronix.de> <80tyoyhxey.fsf_-_@merkur.tec.linutronix.de> <80iq5bqd07.fsf_-_@merkur.tec.linutronix.de> <80vd9ab0d2.fsf@merkur.tec.linutronix.de> <80lja6awlb.fsf@merkur.tec.linutronix.de> Message-ID: <20100624072732.GQ12115@pengutronix.de> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wed, Jun 23, 2010 at 12:10:08PM +0200, John Ogness wrote: > On 2010-06-23, Ivo Clarysse wrote: > > But is it OK to use a regular (non-volatile) variable to communicate > > between interrupt context and the non-interrupt context ? > > In this case, yes. > > > My original patch for i.MX21 used completions instead: > > > > http://lists.infradead.org/pipermail/linux-arm-kernel/2010-April/012694.html > > Ah. It seems you've been through all this before. I wish I had noticed > that thread before. I will need to check more carefully in the future. > > Yes, your original patch achieves the exact same thing. Whether we use > wait_event() with a flag or wait_completion() really is the same > thing. So I guess Sascha can decide what we should do there. > > What I like about your original patch is that only the i.MX21 has the > cost of constantly enabling/disabling the irq line. It adds 5 > cpu_is_mx21() blocks to the code, but will lead to less work for the CPU > on non-i.MX21 boards. Ok, if it's the only way out to have 5 cpu_is_* blocks, then lets go for it. BTW I observed that at least on i.MX27 the latencies introduced by waiting for an interrupt cause a significant performance drop. The driver gets much faster when we just poll all the time. I don't know how this affects system performance otherwise, but it may be a possibility to drop interrupt support at least for i.MX21. I have no idea how long the longest possible time we'd have to poll is though. Sascha -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |