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[104.188.17.28]) by smtp.gmail.com with ESMTPSA id w9sm341994pja.39.2020.07.22.11.03.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Jul 2020 11:03:32 -0700 (PDT) Date: Wed, 22 Jul 2020 11:01:39 -0700 From: Bjorn Andersson To: Mathieu Poirier Cc: Siddharth Gupta , agross@kernel.org, ohad@wizery.com, corbet@lwn.net, linux-remoteproc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, tsoni@codeaurora.org, psodagud@codeaurora.org, rishabhb@codeaurora.org, linux-doc@vger.kernel.org Subject: Re: [PATCH v4 1/2] remoteproc: Add remoteproc character device interface Message-ID: <20200722180139.GA3700915@builder.lan> References: <1594148870-27276-1-git-send-email-sidgup@codeaurora.org> <1594148870-27276-2-git-send-email-sidgup@codeaurora.org> <20200715201839.GA3204081@xps15> <20200715215149.GA3267350@xps15> <81d7514c-727e-b4dc-e4ac-74a25966ccaf@codeaurora.org> <20200721205635.GM2922385@builder.lan> <20200722171841.GA1268891@xps15> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200722171841.GA1268891@xps15> Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Wed 22 Jul 10:18 PDT 2020, Mathieu Poirier wrote: > On Tue, Jul 21, 2020 at 01:56:35PM -0700, Bjorn Andersson wrote: > > On Tue 21 Jul 12:16 PDT 2020, Siddharth Gupta wrote: > > > On 7/15/2020 2:51 PM, Mathieu Poirier wrote: > > > > On Wed, Jul 15, 2020 at 02:18:39PM -0600, Mathieu Poirier wrote: > > > > > On Tue, Jul 07, 2020 at 12:07:49PM -0700, Siddharth Gupta wrote: > > [..] > > > > > > diff --git a/drivers/remoteproc/remoteproc_cdev.c b/drivers/remoteproc/remoteproc_cdev.c > > [..] > > > > > > +int rproc_char_device_add(struct rproc *rproc) > > > > > > +{ > > > > > > + int ret; > > > > > > + dev_t cdevt; > > > > > > + > > > > > > + cdev_init(&rproc->char_dev, &rproc_fops); > > > > > > + rproc->char_dev.owner = THIS_MODULE; > > > > > > + > > > > > > + cdevt = MKDEV(rproc_major, rproc->index); > > > > > > + ret = cdev_add(&rproc->char_dev, cdevt, 1); > > > > Trying this patchset on my side gave me the following splat[1]. After finding > > > > the root case I can't understand how you haven't see it on your side when you > > > > tested the feature. > > > > > > > > [1]. https://pastebin.com/aYTUUCdQ > > > > Mathieu, I've looked at this back and forth. Afaict this implies that > > rproc_major is still 0. Could it be that either alloc_chrdev_region() > > failed or somehow has yet to be called when you hit this point? > > That is exacly what I thought when I first stumbled on this but instrumenting > the code showed otherwise. > > After function rproc_init_cdev() has been called @rproc_major contains the > dynamically allocated major number in the upper 12 bits and the base minor > number in the lower 20 bits. > Ahh, alloc_chrdev_region() actually returns the dev_t, not the major. Too bad that we all name this variable "major" to maximize the confusion. > In rproc_char_device_add() we find this line: > > cdevt = MKDEV(rproc_major, rproc->index); > > Macro MKDEV() builds a device number by shifting @rproc_major by 20 bits to the > left and OR'ing that with @rproc->index. But the device's major number is > already occupying the upper 12bits, so shifthing another 20 bits to the left > makes the major portion of the device number '0'. That is causing cdev_add() to > complain bitterly. > > The right way to do this is: > > cdevt = MKDEV(MAJOR(rproc_major), rproc->index); > Agreed (and let's continue naming it rproc_major, in line with all other drivers - now I know better). Thanks, Bjorn > Once I found the problem I thought about 32/64 bit issues. Since Siddharth is > using a 64bit application processor shifting another 20 bits would still have > yielded a non-zero value. But that can't be since dev_t is a u32 in > linux/types.h. > > As such I can't see how it is possible to not hit that problem on a 64bit > platform. > > > > > > Hey Mathieu, > > > > > > We aren't able to reproduce the error that you are seeing, the splat is > > > coming > > > from the check for whiteout device[1] - which shouldn't happen because of > > > the > > > find_dynamic_major call[2], right? > > > > > > We are successfully seeing all our character device files and able to > > > successfully boot remoteprocs. From what I read and understood about > > > whiteout > > > devices they will be hidden in the fs. > > > > > > Could you provide more details about your configuration and testing? > > > > > > [1]: https://github.com/torvalds/linux/blob/master/fs/char_dev.c#L486 > > > > > > [2]: https://github.com/torvalds/linux/blob/master/fs/char_dev.c#L123 > > > > > > > > > > > > + if (ret < 0) > > > > > > + goto out; > > > > > > + > > > > > > + rproc->dev.devt = cdevt; > > > > > > +out: > > > > > > + return ret; > > > > > > +} > > > > > > + > > > > > > +void rproc_char_device_remove(struct rproc *rproc) > > > > > > +{ > > > > > > + __unregister_chrdev(rproc_major, rproc->index, 1, "remoteproc"); > > > > > > +} > > > > > > + > > > > > > +void __init rproc_init_cdev(void) > > > > > > +{ > > > > > > + int ret; > > > > > > + > > > > > > + ret = alloc_chrdev_region(&rproc_major, 0, NUM_RPROC_DEVICES, "remoteproc"); > > > > > > + if (ret < 0) > > > > > > + pr_err("Failed to alloc rproc_cdev region, err %d\n", ret); > > > > > > +} > > > > > > + > > > > > > +void __exit rproc_exit_cdev(void) > > > > > > +{ > > > > > > + unregister_chrdev_region(MKDEV(rproc_major, 0), NUM_RPROC_DEVICES); > > > > > Please go back to the comment I made on this during my last review and respin. > > > > After digging in the code while debugging the above problem, I don't see how > > > > unregistering the chrdev region the way it is done here would have worked. > > > Since this is compiled statically and not built as a module, we will never > > > exercise the code path, so I will remove it in the next patchset. > > > > > > > You're right Siddharth, since we changed CONFIG_REMOTEPROC to bool it's no longer > > possible to hit remoteproc_exit(), so you can omit this function > > entirely. (And we should clean up the rest of that as well) > > > > [..] > > > > > > diff --git a/include/linux/remoteproc.h b/include/linux/remoteproc.h > > [..] > > > > > > @@ -488,6 +489,8 @@ struct rproc_dump_segment { > > > > > > * @auto_boot: flag to indicate if remote processor should be auto-started > > > > > > * @dump_segments: list of segments in the firmware > > > > > > * @nb_vdev: number of vdev currently handled by rproc > > > > > > + * @char_dev: character device of the rproc > > > > > > + * @cdev_put_on_release: flag to indicate if remoteproc should be shutdown on @char_dev release > > > > > > */ > > > > > > struct rproc { > > > > > > struct list_head node; > > > > > > @@ -523,6 +526,8 @@ struct rproc { > > > > > > int nb_vdev; > > > > > > u8 elf_class; > > > > > > u16 elf_machine; > > > > > > + struct cdev char_dev; > > > > As stated privately, I assumed based on this name that this is a struct > > device related to that character device. So please rename this cdev to > > save me from doing this mistake again. > > > > Thanks, > > Bjorn