From mboxrd@z Thu Jan 1 00:00:00 1970 From: Simon Horman Date: Mon, 27 Dec 2010 01:13:38 +0000 Subject: Re: SDHI polling Message-Id: <20101227011336.GA15786@verge.net.au> List-Id: References: <20101226224506.GD21535@verge.net.au> In-Reply-To: <20101226224506.GD21535@verge.net.au> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-sh@vger.kernel.org On Mon, Dec 27, 2010 at 09:57:50AM +0900, Magnus Damm wrote: > On Mon, Dec 27, 2010 at 9:23 AM, Simon Horman wrote: > > On Mon, Dec 27, 2010 at 07:59:15AM +0900, Magnus Damm wrote: > >> Hi Simon, > >> > >> On Mon, Dec 27, 2010 at 7:45 AM, Simon Horman wrote: > >> > I have it in mind to run the SDHI hardware block in some sort of > >> > polling mode - that is, with interrupts disabled - during early > >> > boot. Does this make any sense? > >> > >> I guess it depends on how early you mean. =) > >> > >> Usually you want to make use of interrupts if they are available, but > >> for really early code there is no interrupt support. So the in-kernel > >> early printk support is implemented without any interrupts for > >> instance. At least this is true for the SCIF driver used by SH and > >> SH-Mobile / R-Mobile, pretty sure it applies to other hardware > >> platforms as well. > >> > >> As for the SDHI version of the MMC loader, I think you should do the > >> same as the MMCIF loader that is present in > >> include/linux/mmc/sh_mmcif.h. As you know it gets compiled into a > >> separate image together with the rest of the zImage loader. No > >> interrupt handling is available in that code, so just implementing > >> things using polling mode is good enough. > >> > >> I'm not 100% sure about U-boot these days, but I wouldn't be surprised > >> if many boot loaders only implement polling. > > > > My plan is to implement the SDHI version of the MMC loader along > > the same lines of the MMCIF version. That plan involves early boot > > where there are no interrupts. > > > > My question was really to ask if from a hardware point of view it is > > possible/reasonable to read from an MMC card using SHDI without interrupts. > > I gather that the answer is yes. > > I believe that is possible, yes. Maybe you can ask around for some > out-of-tree SDHI u-boot excellence to use as an example. I imagine > such code may use polling. =) Good thinking.