Date: Thu, 07 Jun 2007 14:00:54 -0600 (MDT) From: Warner Losh <imp@bsdimp.com> To: nb@synthcom.com Cc: arm@freebsd.org Subject: Re: 4-bit SD Card mode Message-ID: <20070607.140054.74667648.imp@bsdimp.com> In-Reply-To: <20070607123930.E75948@synthcom.com> References: <49754.2001:6f8:101e:0:20e:cff:fe6d:6adb.1181244172.squirrel@webmail.alpha-tierchen.de> <20070607.133456.74668036.imp@bsdimp.com> <20070607123930.E75948@synthcom.com>
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From: Neil Bradley <nb@synthcom.com> Subject: Re: 4-bit SD Card mode Date: Thu, 7 Jun 2007 12:46:37 -0700 (PDT) > > I'm not sure I like this at all. The devices shouldn't be setting up > > the pins for that device. In some cases, they can't know how to do > > that, and this is one of them. The device has no way of knowing if > > all 4 wires are connected, or just 1 and the 'spare' lines are used > > for GPIO. > > Not doing it will irritate more people (i.e. "I'm not getting full speed > out of the SD card). While it's a valid concern, I don't think it's > unrealistic to assume that all 4 DAT lines are hooked up. I've not yet > encountered a design that A) had SD capabilities, B) was only running > single bit because of a lack of GPIOs. I'm not saying that we only hook up the one data. I'm saying that we force the boot loader to do it, or as a fallback a board specific routine. The driver shouldn't be in the business of doing it. My hardware guys are somewhat agressive in their elimination of "unused" lines. We multiplex TX/RX from one of the serial ports to be GPIO lines dynamically at run time depending on what add-in hardware is connected to the box. I want to keep things as flexible as possible because I know that other designs are doing similar "icky" things. Warner
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