From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from metis.ext.pengutronix.de ([2001:6f8:1178:4:290:27ff:fe1d:cc33]) by bombadil.infradead.org with esmtps (Exim 4.76 #1 (Red Hat Linux)) id 1Sqgkb-0005PX-Ea for barebox@lists.infradead.org; Mon, 16 Jul 2012 08:33:54 +0000 Date: Mon, 16 Jul 2012 10:33:21 +0200 From: Sascha Hauer Message-ID: <20120716083321.GC30009@pengutronix.de> References: <025c01cd6323$b85f2220$291d6660$@com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <025c01cd6323$b85f2220$291d6660$@com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: barebox-bounces@lists.infradead.org Errors-To: barebox-bounces+u.kleine-koenig=pengutronix.de@lists.infradead.org Subject: Re: Atmel AT91 SD/MMC clock too fast To: George Pontis Cc: barebox@lists.infradead.org Hi George, On Mon, Jul 16, 2012 at 12:22:13AM -0700, George Pontis wrote: > Due to integer truncation, the calculated divisor for the SD/MMC clock may > be too low, resulting in a clock that is too fast. For example, the > at91sam9g45 is typically run with a master clock at 133 MHz. There is no > divisor possible that will result in a 25 or 50 MHz clock as is typically > used for a SD card. The existing code will set the clock at 33 MHz or 66 MHz > when 25 or 50 MHz is requested. A Kingston class 10 8G SDHC was found to not > work properly at 33 MHz, but did after patching. The patch, in this case, > generated a 22.1 MHz clock ( 133/6 ). This is the same frequency that this > card sees after booting Linux. If a perfect integer division is possible, > the patch will provide an exact clock rate. If not, the frequency will be > the closest possible without exceeding the target. > > The following was based on barebox 2012-07: > > --- a/drivers/mci/atmel_mci.c 2012-07-02 01:31:52.000000000 -0700 > +++ b/drivers/mci/atmel_mci.c 2012-07-15 23:14:02.203872596 -0700 > @@ -76,7 +76,8 @@ > unsigned int clk_in = clk_get_rate(host->clk); > > if (clk_ios > 0) { > - divider = (clk_in / clk_ios) / 2; > + /* don't allow integer truncation to result in too small a > divider */ > + divider = (clk_in + 2 * clk_ios - 1) / (2 * clk_ios); DIV_ROUND_UP(clk_in, clk_ios / 2) instead? 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 | _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox