Re: [RFC PATCH 3/3] gpio: ej1x8: Add GPIO driver for Etron Tech Inc. EJ168/EJ188/EJ198

From: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: linux-usb <linux-usb@vger.kernel.org>,
	linux-pci <linux-pci@vger.kernel.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
	<devicetree@vger.kernel.org>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
	Rob Herring <robh+dt@kernel.org>,
	Bartosz Golaszewski <bgolaszewski@baylibre.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Bjorn Helgaas <bhelgaas@google.com>
Subject: Re: [RFC PATCH 3/3] gpio: ej1x8: Add GPIO driver for Etron Tech Inc. EJ168/EJ188/EJ198
Date: Wed, 7 Oct 2020 21:44:51 +0200	[thread overview]
Message-ID: <CAFBinCCLubmDvxfabQHx2-ucgAsm1NArMUrtPx-UA2nX5xoFFA@mail.gmail.com> (raw)
In-Reply-To: <CACRpkdZo-U_cAhbKb4E+d+p+5FenXkGYW0RXxyk4M5uyEPCpzw@mail.gmail.com>

Hi Linus,

On Wed, Oct 7, 2020 at 11:29 AM Linus Walleij <linus.walleij@linaro.org> wrote:
>
> Hi Martin,
>
> thanks for your patch!
thank you for reviewing the whole series!

> As noted on the earlier patches I think this should be folded into the
> existing XHCI USB driver in drivers/usb/host/xhci-pci.c or, if that
> gets messy, as a separate bolt-on, something like
> xhci-pci-gpio.[c|h] in the drivers/usb/host/* directory.
> You can use a Kconfig symbol for the GPIO portions or not.
OK, I will do that if there are no objections from other developers
I am intending to place the relevant code in xhci-pci-etron.c, similar
to what we already have with xhci-pci-renesas.c

[...]
> This should not be necessary. Tie the GPIO state into the PCI device
> driver state, possibly using some #ifdefs.
>
> > +static u8 ej1x8_gpio_shift(unsigned int gpio, u8 mask)
> > +{
> > +       return (gpio * fls(mask));
> > +}
> > +
> > +static u8 ej1x8_gpio_mask(unsigned int gpio, u8 mask)
> > +{
> > +       return mask << ej1x8_gpio_shift(gpio, mask);
> > +}
>
> This looks a bit like regmap but trying to use regmap for this
> would probably be overengineering.
the problem is also the "INIT" register which needs to be set before
writing the registers

> Looking at the code I get annoyed that it uses the config space to
> manipulate the GPIOs, else you could have used GPIO_GENERIC
> but now you can't, how typical.
I think this won't work in practice because of the EJ1X8_GPIO_CTRL for
which we have to read from bits [7:0] but write to bits [23:16]
due to this (and the INIT register as mentioned above) I did not
consider GPIO_GENERIC any further

> Other than that the code looks nice, but fold it into the USB
> host driver somehow unless there is a compelling argument
> as to why not.
will do so, thanks!

Best regards,
Martin