From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tom Rini Date: Fri, 18 May 2012 09:11:57 -0700 Subject: [U-Boot] [RFC] Make i2c probe opt-outable? In-Reply-To: <201205172248.20143.vapier@gentoo.org> References: <20120517184345.GA23562@bill-the-cat> <201205172248.20143.vapier@gentoo.org> Message-ID: <4FB674CD.8030502@ti.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de On 05/17/2012 07:48 PM, Mike Frysinger wrote: > On Thursday 17 May 2012 14:43:45 Tom Rini wrote: >> I'd like to propose making 'i2c probe' be a command that is >> opt-out'able. In the Linux Kernel the notion of probing for devices was >> abandoned a while ago due to, in short, devices misbehaving when >> randomly poked at. Over in omap24xx_i2c land we changed our probe >> method a while ago from an attempted read to an attempted write as some >> i2c devices would NAK the read. But now with the am33xx SoM family we >> have a new issue which is that attempting to write to an address doesn't >> immediately issue a NAK so probe sees all addresses as valid and in turn >> leaves the bus upset. I've worked around this for now by making >> i2c_probe use the read method instead, only on am33xx (so most devices >> would be spotted, but the ones that caused the initial change would not >> show up). But a possibly better solution is to just make the i2c probe >> command not implemented for am33xx (as you don't have to run i2c probe >> to try and use your device). > > i've always seen the "i2c probe" command as a debugging tool, not something > that you need to do to make things work. so along those lines, isn't it > already optional ? if you don't like it, don't run it :). Including a command that doesn't work and saying "ah, just don't use that" is asking for trouble. I'm going down the "what changed in the IP block, really" rat-hole now (since I've got the original test working). But still, the kernel decided i2c probing is dangerous/unreliable, maybe we should follow, or at least allow boards to follow? -- Tom