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Sun, 18 Oct 2020 17:55:12 -0700 (PDT) From: Coiby Xu X-Google-Original-From: Coiby Xu Date: Mon, 19 Oct 2020 08:54:12 +0800 To: =?utf-8?Q?Barnab=C3=A1s_P=C5=91cze?= Cc: "linux-input@vger.kernel.org" , Helmut Stult , "stable@vger.kernel.org" , Jiri Kosina , Benjamin Tissoires , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v2] HID: i2c-hid: add polling mode based on connected GPIO chip's pin status Message-ID: <20201019005412.rifxrvpdxu574jag@Rk> References: <20201016131335.8121-1-coiby.xu@gmail.com> <20201017004556.kuoxzmbvef4yr3kg@Rk> <20201017140541.fggujaz2klpv3cd5@Rk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-input@vger.kernel.org On Sat, Oct 17, 2020 at 02:58:13PM +0000, Barnabás Pőcze wrote: >> [...] >> >> >> +static int get_gpio_pin_state(struct irq_desc *irq_desc) >> >> >> +{ >> >> >> + struct gpio_chip *gc = irq_data_get_irq_chip_data(&irq_desc->irq_data); >> >> >> + >> >> >> + return gc->get(gc, irq_desc->irq_data.hwirq); >> >> >> +} >> >> >> + >> >> >> +static bool interrupt_line_active(struct i2c_client *client) >> >> >> +{ >> >> >> + unsigned long trigger_type = irq_get_trigger_type(client->irq); >> >> >> + struct irq_desc *irq_desc = irq_to_desc(client->irq); >> >> >> + >> >> >> + /* >> >> >> + * According to Windows Precsiontion Touchpad's specs >> >> >> + * https://docs.microsoft.com/en-us/windows-hardware/design/component-guidelines/windows-precision-touchpad-device-bus-connectivity, >> >> >> + * GPIO Interrupt Assertion Leve could be either ActiveLow or >> >> >> + * ActiveHigh. >> >> >> + */ >> >> >> + if (trigger_type & IRQF_TRIGGER_LOW) >> >> >> + return !get_gpio_pin_state(irq_desc); >> >> >> + >> >> >> + return get_gpio_pin_state(irq_desc); >> >> >> +} >> >> > >> >> >Excuse my ignorance, but I think some kind of error handling regarding the return >> >> >value of `get_gpio_pin_state()` should be present here. >> >> > >> >> What kind of errors would you expect? It seems (struct gpio_chip *)->get >> >> only return 0 or 1. >> >> > >> > >> >I read the code of a couple gpio chips and - I may be wrong, but - it seems they >> >can return an arbitrary errno. >> > >> I thought all GPIO chip return 0 or 1 since !!val is returned. I find >> an example which could return negative value, >> > >Yes, when a function returns `int`, there is a very high chance that the return >value may be an errno. > > >> > >> >> >> + >> >> >> +static int i2c_hid_polling_thread(void *i2c_hid) >> >> >> +{ >> >> >> + struct i2c_hid *ihid = i2c_hid; >> >> >> + struct i2c_client *client = ihid->client; >> >> >> + unsigned int polling_interval_idle; >> >> >> + >> >> >> + while (1) { >> >> >> + /* >> >> >> + * re-calculate polling_interval_idle >> >> >> + * so the module parameters polling_interval_idle_ms can be >> >> >> + * changed dynamically through sysfs as polling_interval_active_us >> >> >> + */ >> >> >> + polling_interval_idle = polling_interval_idle_ms * 1000; >> >> >> + if (test_bit(I2C_HID_READ_PENDING, &ihid->flags)) >> >> >> + usleep_range(50000, 100000); >> >> >> + >> >> >> + if (kthread_should_stop()) >> >> >> + break; >> >> >> + >> >> >> + while (interrupt_line_active(client)) { >> >> > >> >> >I realize it's quite unlikely, but can't this be a endless loop if data is coming >> >> >in at a high enough rate? Maybe the maximum number of iterations could be limited here? >> >> > >> >> If we find HID reports are constantly read and send to front-end >> >> application like libinput, won't it help expose the problem of the I2C >> >> HiD device? >> >> > >> > >> >I'm not sure I completely understand your point. The reason why I wrote what I wrote >> >is that this kthread could potentially could go on forever (since `kthread_should_stop()` >> >is not checked in the inner while loop) if the data is supplied at a high enough rate. >> >That's why I said, to avoid this problem, only allow a certain number of iterations >> >for the inner loop, to guarantee that the kthread can stop in any case. >> > >> I mean if "data is supplied at a high enough rate" does happen, this is >> an abnormal case and indicates a bug. So we shouldn't cover it up. We >> expect the user to report it to us. >> > > >I agree in principle, but if this abnormal case ever occurs, that'll prevent >this module from being unloaded since `kthread_stop()` will hang because the >thread is "stuck" in the inner loop, never checking `kthread_should_stop()`. >That's why I think it makes sense to only allow a certain number of operations >for the inner loop, and maybe show a warning if that's exceeded: > > for (i = 0; i < max_iter && interrupt_line_active(...); i++) { > .... > } > > WARN_ON[CE](i == max_iter[, "data is coming in at an unreasonably high rate"]); > >or something like this, where `max_iter` could possibly be some value dependent on >`polling_interval_active_us`, or even just a constant. > Thank you for suggesting this approach! It seems it would add a bit of complexity to detect this situation which could introduce other bugs. I did a experiment of creating a kthread that will loop forever and found the rebooting process wasn't stalled. I don't expect user to load&unload this module. So the end user could not notice this problem so my rationale is invalid. Thus I would be prefer to check `kthread_should_stop()` in the inner while loop instead. > >> >> >> + i2c_hid_get_input(ihid); >> >> >> + usleep_range(polling_interval_active_us, >> >> >> + polling_interval_active_us + 100); >> >> >> + } >> >> >> + >> >> >> + usleep_range(polling_interval_idle, >> >> >> + polling_interval_idle + 1000); >> >> >> + } >> >> >> + >> >> >> + do_exit(0); >> >> >> + return 0; >> >> >> +} >> [...] >> Thank you for offering your understandings on this patch. When I'm going >> to submit next version, I will add a "Signed-off-by" tag with your name >> and email, does it look good to you? >> [...] > >I'm not sure if that follows proper procedures. > > "The sign-off is a simple line at the end of the explanation for the patch, which > certifies that you wrote it or otherwise have the right to pass it on as an > open-source patch."[1] > >I'm not the author, nor co-author, nor am I going to pass this patch on, so I don't >think that's appropriate. > >Furthermore, please note that > > "[...] you may optionally add a Cc: tag to the patch. **This is the only tag which > might be added without an explicit action by the person it names** - but it should > indicate that this person was copied on the patch."[2] > (emphasis mine) > You have been directly contributing to this patch because several improvements of next version are from you. I experienced a similar situation when submitting patches for QEMU. The only difference is that the feedbacks on the QEMU patches were also given in the format of patch. Or do you think a reviewed-by tag from you after you think the next version is of production quality is a better way to credit you? > >Regards, >Barnabás Pőcze > > >[1]: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#sign-your-work-the-developer-s-certificate-of-origin >[2]: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#when-to-use-acked-by-cc-and-co-developed-by -- Best regards, Coiby