From: Stephen Warren <swarren@wwwdotorg.org>
To: Laxman Dewangan <ldewangan@nvidia.com>,
Linus Walleij <linus.walleij@linaro.org>
Cc: Alexandre Courbot <gnurou@gmail.com>,
Thierry Reding <thierry.reding@gmail.com>,
"linux-gpio@vger.kernel.org" <linux-gpio@vger.kernel.org>,
"linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH V5 0/4] gpio: tegra: Cleanups and support for debounce
Date: Tue, 3 May 2016 09:59:14 -0600 [thread overview]
Message-ID: <5728CAD2.9050701@wwwdotorg.org> (raw)
In-Reply-To: <5727A535.2060808@nvidia.com>
On 05/02/2016 01:06 PM, Laxman Dewangan wrote:
>
> On Tuesday 03 May 2016 12:14 AM, Stephen Warren wrote:
>> On 05/02/2016 11:58 AM, Laxman Dewangan wrote:
>>>
>>>
>>> Toggling OE bit is something emulating the open drain here.
>>
>> From the perspective of the external HW that's attached to the GPIO, I
>> believe there's no difference.
>>
>>> I think idea is that when we configure the pin in open drain then it
>>> should be automatically handled by HW when we want to set pin state
>>> high or low. When we set low, the pin should be driven and when high
>>> then it should be tristated input. We should not need any direction bit
>>> setting.
>>
>> I don't imagine anything in the kernel cares, so long as the correct
>> logic level is present on the pin based on whatever GPIO API was last
>> called.
>>
>> I'd be very surprised if there wasn't hardware that could only
>> implement open-drain by this "emulation" method, so I'd be very
>> surprised if something prohibited that implementation style.
>>
>
> The emulation method implemented just to not drive high for open drain.
> Recently, proper callback added for hw control for open drain and hence
> emulation method is not needed for such HW.
>
> I think if HW support the callback to implement the open drain then use
> the HW method otherwise fallback to emulation method.
I don't see any benefit to that. It makes the code more complex without
enabling any more features.
For reference, on Tegra124 and earlier, very few pins have open-drain
control in HW (pinmux) whereas you can emulate it in the GPIO module for
any pin. In Tegra210 and Tegra186, many pins have open-drain control in
HW (pinmux) yet a good number still don't, yet you can still emulate
this in the GPIO module for any pin.
prev parent reply other threads:[~2016-05-03 15:59 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-25 10:38 [PATCH V5 0/4] gpio: tegra: Cleanups and support for debounce Laxman Dewangan
2016-04-25 10:38 ` [PATCH V5 1/4] gpio: tegra: Don't open code of_device_get_match_data() Laxman Dewangan
2016-04-29 8:59 ` Linus Walleij
2016-04-25 10:38 ` [PATCH V5 2/4] gpio: tegra: Make of_device_id compatible data to constant Laxman Dewangan
2016-04-29 9:00 ` Linus Walleij
2016-04-25 10:38 ` [PATCH V5 3/4] gpio: tegra: Get rid of all file scoped global variables Laxman Dewangan
2016-04-29 9:01 ` Linus Walleij
2016-04-25 10:38 ` [PATCH V5 4/4] gpio: tegra: Add support for gpio debounce Laxman Dewangan
2016-04-28 5:58 ` Alexandre Courbot
2016-04-29 9:03 ` Linus Walleij
2016-04-29 9:07 ` [PATCH V5 0/4] gpio: tegra: Cleanups and support for debounce Linus Walleij
2016-04-29 9:20 ` Laxman Dewangan
2016-04-30 11:07 ` Linus Walleij
2016-05-02 6:44 ` Laxman Dewangan
2016-05-02 16:12 ` Stephen Warren
2016-05-02 17:58 ` Laxman Dewangan
2016-05-02 18:44 ` Stephen Warren
2016-05-02 19:06 ` Laxman Dewangan
2016-05-03 15:59 ` Stephen Warren [this message]
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