From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DD9A37E792; Wed, 25 Jun 2025 09:01:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750842101; cv=none; b=ifo9NZ2Ng0YW2qk8Owyqx6J+gehrvQyVukJc3hsLXulN1vO33RoBJ9nmxIT6Q8bKGrpBjaaYIMtSkS3shjfg2mqRcrPkoJzULyfQ8DfkRS2iTRcgJrEgNisq5pJLWed9r9Ghk+lE2YruFP6vuwPOGGDKKzrRn+gxgpvV81+19dA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750842101; c=relaxed/simple; bh=OhdgF55PyBEbfC8aXgc9N1rHxO4doVes6/sM5CeG1ZU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=teMKDJDYBYBSDjpcayoA+WGPjv6AhAG0e6k1aHafTrr4D4gh5JAr953xLw6VLB0xuPVSLSovBLdYyJwf18FbI6xlKh8eS+UIr3ptSG9lX2SntSZnzk4zFEHXvkoP/u/es2kKujeL4AJUdQ4kPa8si5vG1llI7iHcXmPcI7g4Uok= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=kmWaOFjU; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="kmWaOFjU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EA9ADC4CEEA; Wed, 25 Jun 2025 09:01:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1750842100; bh=OhdgF55PyBEbfC8aXgc9N1rHxO4doVes6/sM5CeG1ZU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=kmWaOFjUT1wMib2gJdif3D7Ejx4H1upQdwnyg4IgRfaVtd5UkCyhMfOC76/FUKCgd vxAHh5XhTgPH4e9ON+kNB4QIpDFQ/8mWmCl83/GHhLyyjDp1vZvkEaecgSx8QtvX+a Sb6medYCTIPOU5fcM/Ff+yprIo/QdiK0Mjr3VOBABQvUXWYbkQksv7UAhdXb0ianvJ BRt0NEUZp8EKImSvLzdWddbpxzJqOo0edMBk+gtjyzAoRVhtTQMPeV+i6TGDdniD03 uFi8a7/s5Fa5nOtywCjlBDJwWxf2Gmh8lUCG9O7yMGxOobFxqR4FXbXy6nSJAlQVcO wJyii3Wxvv+JA== Date: Wed, 25 Jun 2025 10:01:33 +0100 From: Lee Jones To: Ming Yu Cc: linus.walleij@linaro.org, brgl@bgdev.pl, andi.shyti@kernel.org, mkl@pengutronix.de, mailhol.vincent@wanadoo.fr, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, wim@linux-watchdog.org, linux@roeck-us.net, jdelvare@suse.com, alexandre.belloni@bootlin.com, linux-kernel@vger.kernel.org, linux-gpio@vger.kernel.org, linux-i2c@vger.kernel.org, linux-can@vger.kernel.org, netdev@vger.kernel.org, linux-watchdog@vger.kernel.org, linux-hwmon@vger.kernel.org, linux-rtc@vger.kernel.org, linux-usb@vger.kernel.org, Ming Yu Subject: Re: [PATCH v12 1/7] mfd: Add core driver for Nuvoton NCT6694 Message-ID: <20250625090133.GP795775@google.com> References: <20250612140041.GF381401@google.com> <20250612152313.GP381401@google.com> <20250613131133.GR381401@google.com> <20250619115345.GL587864@google.com> <20250619152814.GK795775@google.com> Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Fri, 20 Jun 2025, Ming Yu wrote: > Lee Jones 於 2025年6月19日 週四 下午11:28寫道： > > > > On Thu, 19 Jun 2025, Ming Yu wrote: > > > > > Lee Jones 於 2025年6月19日 週四 下午7:53寫道： > > > > > > > > On Fri, 13 Jun 2025, Ming Yu wrote: > > > > > > > > > Lee Jones 於 2025年6月13日 週五 下午9:11寫道： > > > > > > > > > > > > On Fri, 13 Jun 2025, Ming Yu wrote: > > > > > > > > > > > > > Lee Jones 於 2025年6月12日 週四 下午11:23寫道： > > > > > > > > > > > > > > > > On Thu, 12 Jun 2025, Ming Yu wrote: > > > > > > > > > > > > > > > > > Dear Lee, > > > > > > > > > > > > > > > > > > Thank you for reviewing, > > > > > > > > > > > > > > > > > > Lee Jones 於 2025年6月12日 週四 下午10:00寫道： > > > > > > > > > > > > > > > > > > > ... > > > > > > > > > > > +static const struct mfd_cell nct6694_devs[] = { > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 0), > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 1), > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 2), > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 3), > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 4), > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 5), > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 6), > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 7), > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 8), > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 9), > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 10), > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 11), > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 12), > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 13), > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 14), > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-gpio", NULL, NULL, 0, 15), > > > > > > > > > > > + > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-i2c", NULL, NULL, 0, 0), > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-i2c", NULL, NULL, 0, 1), > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-i2c", NULL, NULL, 0, 2), > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-i2c", NULL, NULL, 0, 3), > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-i2c", NULL, NULL, 0, 4), > > > > > > > > > > > + MFD_CELL_BASIC("nct6694-i2c", NULL, NULL, 0, 5), > > > > > > > > > > > > > > > > > > > > Why have we gone back to this silly numbering scheme? > > > > > > > > > > > > > > > > > > > > What happened to using IDA in the child driver? > > > > > > > > > > > > > > > > > > > > > > > > > > > > In a previous version, I tried to maintain a static IDA in each > > > > > > > > > sub-driver. However, I didn’t consider the case where multiple NCT6694 > > > > > > > > > devices are bound to the same driver — in that case, the IDs are not > > > > > > > > > fixed and become unusable for my purpose. > > > > > > > > > > > > > > > > Not sure I understand. > > > > > > > > > > > > > > > > > > > > > > As far as I know, if I maintain the IDA in the sub-drivers and use > > > > > > > multiple MFD_CELL_NAME("nct6694-gpio") entries in the MFD, the first > > > > > > > NCT6694 device bound to the GPIO driver will receive IDs 0~15. > > > > > > > However, when a second NCT6694 device is connected to the system, it > > > > > > > will receive IDs 16~31. > > > > > > > Because of this behavior, I switched back to using platform_device->id. > > > > > > > > > > > > Each of the devices will probe once. > > > > > > > > > > > > The first one will be given 0, the second will be given 1, etc. > > > > > > > > > > > > Why would you give multiple IDs to a single device bound to a driver? > > > > > > > > > > > > > > > > The device exposes multiple peripherals — 16 GPIO controllers, 6 I2C > > > > > adapters, 2 CAN FD controllers, and 2 watchdog timers. Each peripheral > > > > > is independently addressable, has its own register region, and can > > > > > operate in isolation. The IDs are used to distinguish between these > > > > > instances. > > > > > For example, the GPIO driver will be probed 16 times, allocating 16 > > > > > separate gpio_chip instances to control 8 GPIO lines each. > > > > > > > > > > If another device binds to this driver, it is expected to expose > > > > > peripherals with the same structure and behavior. > > > > > > > > I still don't see why having a per-device IDA wouldn't render each > > > > probed device with its own ID. Just as you have above. > > > > > > > > > > For example, when the MFD driver and the I2C sub-driver are loaded, > > > connecting the first NCT6694 USB device to the system results in 6 > > > nct6694-i2c platform devices being created and bound to the > > > i2c-nct6694 driver. These devices receive IDs 0 through 5 via the IDA. > > > > > > However, when a second NCT6694 USB device is connected, its > > > corresponding nct6694-i2c platform devices receive IDs 6 through 11 — > > > instead of 0 through 5 as I originally expected. > > > > > > If I've misunderstood something, please feel free to correct me. Thank you! > > > > In the code above you register 6 I2C devices. Each device will be > > assigned a platform ID 0 through 5. The .probe() function in the I2C > > driver will be executed 6 times. In each of those calls to .probe(), > > instead of pre-allocating a contiguous assignment of IDs here, you > > should be able to use IDA in .probe() to allocate those same device IDs > > 0 through 5. > > > > What am I missing here? > > > > You're absolutely right in the scenario where a single NCT6694 device > is present. However, I’m wondering how we should handle the case where > a second or even third NCT6694 device is bound to the same MFD driver. > In that situation, the sub-drivers using a static IDA will continue > allocating increasing IDs, rather than restarting from 0 for each > device. How should this be handled? I'd like to see the implementation of this before advising. In such a case, I assume there would be a differentiating factor between the two (or three) devices. You would then use that to decide which IDA would need to be incremented. However, Greg is correct. Hard-coding look-ups for userspace to use sounds like a terrible idea. -- Lee Jones [李琼斯]