From: Doug Berger <opendmb@gmail.com>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Bartosz Golaszewski <brgl@bgdev.pl>,
Phil Elwell <phil@raspberrypi.com>, Rob Herring <robh@kernel.org>,
Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
Conor Dooley <conor+dt@kernel.org>,
Florian Fainelli <florian.fainelli@broadcom.com>,
bcm-kernel-feedback-list@broadcom.com,
linux-gpio@vger.kernel.org, devicetree@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] gpio: of: support gpio-ranges for multiple gpiochip devices
Date: Fri, 3 May 2024 13:21:25 -0700 [thread overview]
Message-ID: <45b7742c-9cde-4238-9c2c-c75dfbe9d8f3@gmail.com> (raw)
In-Reply-To: <CACRpkda4v6Nu8V3MVamDpfs4qnc89e8Vd8fSyaNsqJQ40GQqZg@mail.gmail.com>
On 5/3/2024 1:25 AM, Linus Walleij wrote:
> Hi Dough,
>
> thanks for your patch!
Thanks for your review!
>
> I'm a bit confused here:
"Communication is hard" and I may be confused about your confusion, but
hopefully we can work it out.
>
> On Wed, Apr 24, 2024 at 8:51 PM Doug Berger <opendmb@gmail.com> wrote:
>
>
>> + /* Ignore ranges outside of this GPIO chip */
>> + if (pinspec.args[0] >= (chip->offset + chip->ngpio))
>> + continue;
>> + if (pinspec.args[0] + pinspec.args[2] <= chip->offset)
>> + continue;
>
> Here pinspec.args[0] and [2] comes directly from the device tree.
>
> The documentation in Documentation/devicetree/bindings/gpio/gpio.txt
> says:
>
>> 2.2) Ordinary (numerical) GPIO ranges
>> -------------------------------------
>>
>> It is useful to represent which GPIOs correspond to which pins on which pin
>> controllers. The gpio-ranges property described below represents this with
>> a discrete set of ranges mapping pins from the pin controller local number space
>> to pins in the GPIO controller local number space.
>>
>> The format is: <[pin controller phandle], [GPIO controller offset],
>> [pin controller offset], [number of pins]>;
>>
>> The GPIO controller offset pertains to the GPIO controller node containing the
>> range definition.
I think we are in agreement here. For extra clarity, I will add that in
my understanding pinspec.args[0] corresponds to [GPIO controller offset]
and pinspec.args[2] corresponds to [number of pins].
>
> So I do not understand how pinspec[0] and [2] can ever be compared
> to something involving chip->offset which is a Linux-specific offset.
>
> It rather looks like you are trying to accomodate the Linux numberspace
> in the ranges, which it was explicitly designed to avoid.
The struct gpio_chip documentation in include/linux/gpio/driver.h says:
> * @offset: when multiple gpio chips belong to the same device this
> * can be used as offset within the device so friendly names can
> * be properly assigned.
It is my understanding that this value represents the offset of a
gpiochip relative to the GPIO controller device defined by the GPIO
controller node in device tree. This puts it in the same number space as
[GPIO controller offset]. I believe it was introduced for the specific
purpose of translating [GPIO controller offset] values into
Linux-specific offsets, which is why it is being reused for that purpose
in this patch.
For GPIO Controllers that contain a single gpiochip the 'offset' member
is 0 and the device tree node offsets can be applied directly to the
gpiochip. However, when a GPIO Controller contains multiple gpiochips,
the device tree node offsets must be translated to each individual gpiochip.
>
> I just don't get it.
>
> So NACK until I understand what is going on here.
>
> Yours,
> Linus Walleij
I hope it makes sense now, but if not please help me understand what I
may be missing.
Thanks,
Doug
next prev parent reply other threads:[~2024-05-03 20:21 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-24 18:50 [PATCH 0/3] gpio: brcmstb: add support for gpio-ranges Doug Berger
2024-04-24 18:50 ` [PATCH 1/3] dt-bindings: gpio: brcmstb: add gpio-ranges Doug Berger
2024-04-24 23:11 ` Florian Fainelli
2024-04-25 6:59 ` Krzysztof Kozlowski
2024-05-03 7:57 ` Linus Walleij
2024-04-24 18:50 ` [PATCH 2/3] gpio: of: support gpio-ranges for multiple gpiochip devices Doug Berger
2024-04-24 23:14 ` Florian Fainelli
2024-04-26 7:32 ` Bartosz Golaszewski
2024-05-03 8:25 ` Linus Walleij
2024-05-03 20:21 ` Doug Berger [this message]
2024-05-05 12:25 ` Bartosz Golaszewski
2024-05-06 7:03 ` Linus Walleij
2024-05-06 7:02 ` Linus Walleij
2024-04-24 18:50 ` [PATCH 3/3] gpio: brcmstb: add support for gpio-ranges Doug Berger
2024-04-24 23:12 ` Florian Fainelli
2024-04-26 7:33 ` [PATCH 0/3] " Bartosz Golaszewski
2024-05-03 8:29 ` Linus Walleij
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