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([2600:1700:e321:62f0:da43:aeff:fecc:bfd5]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7490a621ceasm252302b3a.97.2025.06.19.09.58.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 19 Jun 2025 09:58:06 -0700 (PDT) Sender: Guenter Roeck Message-ID: <644dfd66-ad30-47cb-9ec4-50d9a003433b@roeck-us.net> Date: Thu, 19 Jun 2025 09:58:04 -0700 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v12 1/7] mfd: Add core driver for Nuvoton NCT6694 To: Greg KH , Ming Yu Cc: Lee Jones , 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, 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 References: <20250612140041.GF381401@google.com> <20250612152313.GP381401@google.com> <20250613131133.GR381401@google.com> <20250619115345.GL587864@google.com> <20250619152814.GK795775@google.com> <2025061910-skies-outgoing-89cc@gregkh> Content-Language: en-US From: Guenter Roeck Autocrypt: addr=linux@roeck-us.net; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 6/19/25 09:20, Greg KH wrote: > On Fri, Jun 20, 2025 at 12:03:01AM +0800, 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? > > What is wrong with increasing ids? The id value means nothing, they > just have to be unique. > Unless they are used in the client driver as index into an array, as in "this is the Nth instance of this device for this chip". There has to be _some_ means to pass N to the client driver. Guenter