Re: [PATCH v5 1/3] mfd: ch341: add core driver for the WCH CH341 in I2C/SPI/GPIO mode

From: Frank Zago <frank@zago.net>
To: Lee Jones <lee.jones@linaro.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-kernel@vger.kernel.org,
	Bartosz Golaszewski <bgolaszewski@baylibre.com>,
	Wolfram Sang <wsa@kernel.org>, Johan Hovold <johan@kernel.org>,
	linux-usb@vger.kernel.org,
	Linus Walleij <linus.walleij@linaro.org>,
	linux-gpio@vger.kernel.org, linux-i2c@vger.kernel.org
Subject: Re: [PATCH v5 1/3] mfd: ch341: add core driver for the WCH CH341 in I2C/SPI/GPIO mode
Date: Wed, 15 Jun 2022 20:18:47 -0500	[thread overview]
Message-ID: <af03596e-f06c-9c23-1904-34317e25620a@zago.net> (raw)
In-Reply-To: <YmgDID8pRYDFK8vi@google.com>

Hi Lee,

>> +	dev->ep_in = endpoints[0].desc.bEndpointAddress;
>> +	dev->ep_out = endpoints[1].desc.bEndpointAddress;
>> +	dev->ep_intr = endpoints[2].desc.bEndpointAddress;
>> +	dev->ep_intr_interval = endpoints[2].desc.bInterval;
>> +
>> +	usb_set_intfdata(iface, dev);
>> +
>> +	rc = mfd_add_hotplug_devices(&iface->dev, ch341_devs,
> 
> Why are you using 'hotplug' here?

I replaced with mfd_add_devices, however I'm not sure what the difference
 is since mfd_add_hotplug_devices() is just a helper with less parameters.
That's what the viperboard driver does; I just copied since both devices 
are similar in functionality.

> 
> ch341_devs is empty right?
> 
> So no child devices are registered.
> 
> In which case this is not (yet) an MFD and cannot be accepted.
> 
> Please add the children.
> 
>> +				     ARRAY_SIZE(ch341_devs));
>> +	if (rc) {
>> +		rc = dev_err_probe(&iface->dev, rc,
>> +				   "Failed to add mfd devices to core\n");
> 
> I'm not even sure what this means.  Should be:
> 
> "Failed to register child devices\n"

Changed. The original string was also from the viperboard driver.

> 
>> +MODULE_DESCRIPTION("CH341 USB to I2C/SPI/GPIO adapter");
> 
> Is it?  What makes it one of those?

That's what this chip does, in addition to UART and printer modes. See patch 4.

Frank.