From mboxrd@z Thu Jan 1 00:00:00 1970 From: Real Name Subject: Re: EPROBE_DEFER and how it is supposed to work Date: Wed, 10 Sep 2014 11:08:45 +0800 Message-ID: <20140910030845.GA9846@name.redhat.com> References: Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; bh=zl9+x1Kq/hhlcfxs2Fkjk75Xk+bw6G63vBhRF95g+hc=; b=Lq6LUyPIn10Dbr6P227xvYVY/fpJwa7f4+gNXqncEbUszgpUgY/oQBN60oJVoKujyN 7BOSrwC8V19Z05zqpbmyqaxGUVGfguMfJRayEjfj/6JrbBsPGoZ/HDjDUUWuf8sQDmu+ k3lkUSnaIw/OMQW2iWeseQBmANKy5wdxR9NXMcYP6fTGLdrTFE4nok67QIAK/g2KlCG2 55F3bL9n/Y2oI3/865q4Dg+75yeFK1A7dHR3yvhP3hCLJ71hbbC8RY9EVVUi58ISqzVd sTV2xXN1ir3DK5QC0AbTzyCUBpjMzfxkieOKIm0kvlVVvVExHy1QE9+7c7+OJdhzouDq G7Sw== Content-Disposition: inline In-Reply-To: Sender: linux-newbie-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Rajat Jain Cc: kernelnewbies , "linux-newbie@vger.kernel.org" On Tue, Sep 09, 2014 at 06:26:27PM +0000, Rajat Jain wrote: > Hi, > > I'm not a newbie, but I am trying to understand the semantics of deferred probing. > > My question is generic, but for an example: > > Let's say I have a platform driver "A" for a device "a", that requires device "b" (controlled by driver "B") to be operational first. Both A &B can be built as part of kernel, or as modules independently. As far as I could tell, there is no way to specify the ORDER in which the drivers' probe routines should be called. I took a look at modprobe / depmod, but it seems to be of relevance for modules only that are loaded from user space. My questions: > > 1) Is there a way to specify that "Kernel should call A's probe routine only after B's probe routine"? You can ask module A to load the required module B. For example, lib/textsearch.c:textsearch_prepare -> lookup_ts_algo lookup_ts_algo will load ts_bm.ko/ts_fsm.ko/ts_kmp.ko as required. > > 2) How I currently do this: In A's probe routine, I currently check if the device "b" is available. If not, I return -EPROBE_DEFER. This mostly works ok. However, I'm curious about the case where the driver B is not built as part of the kernel but A is. After getting an _EPROB_DEFER from a B's probe routine, when will the kernel try again? And for how long would it keep on trying? I verified that if I load the driver B manually from user space, the A's probe routine does not get called (if it gets called now - it would have returned success!). > > Thanks, > > Rajat > > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies@kernelnewbies.org > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies -- To unsubscribe from this list: send the line "unsubscribe linux-newbie" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.linux-learn.org/faqs