From: Wolfram Sang <wsa@the-dreams.de>
To: Phil Reid <preid@electromag.com.au>
Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>,
linux-i2c@vger.kernel.org, linux-renesas-soc@vger.kernel.org,
kernel@pengutronix.de,
Jarkko Nikula <jarkko.nikula@linux.intel.com>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Mika Westerberg <mika.westerberg@linux.intel.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH/RFT 1/6] i2c: designware: use open drain for recovery GPIO
Date: Tue, 17 Jul 2018 11:09:20 +0200 [thread overview]
Message-ID: <20180717090920.zy6lkeqlcewhrfs5@ninjato> (raw)
In-Reply-To: <daaf702b-642f-e0fd-6a2e-7f0f817efba3@electromag.com.au>
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Hi Phil,
> > - gpio = devm_gpiod_get(dev->dev, "scl", GPIOD_OUT_HIGH);
> > + gpio = devm_gpiod_get(dev->dev, "scl", GPIOD_OUT_HIGH_OPEN_DRAIN);
> > if (IS_ERR(gpio)) {
> > r = PTR_ERR(gpio);
> > if (r == -ENOENT || r == -ENOSYS)
> >
>
> This was intentional. The gpio we use to drive the i2c line is implemented in an
> FPGA and signals a buffer attached to the GPIO to drive scl OPEN drain. The GPIO is output
> only.
So, it is not possible to read SCL status then? Hmm, currently a working
get_scl is required...
> The gpio setup can still specify the the GPIO be allocated OPEN drain if someone wishes
> to use a "smarter" gpio.
>
> So while the scl is open drain, there may be hardware in between that isn't.
> What would the correct way be to deal with that now?
Well, I don't know much about this IP core and how/where it is used. I
just wonder what happens if another user comes along using an
open-drain GPIO. Is that possible?
I assume it is the same with SDA? Non open-drain? Output only?
Regards,
Wolfram
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next prev parent reply other threads:[~2018-07-17 9:09 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-13 21:09 [PATCH/RFT 0/6] i2c: recovery: fix GPIO usage for recovery Wolfram Sang
2018-07-13 21:09 ` [PATCH/RFT 1/6] i2c: designware: use open drain for recovery GPIO Wolfram Sang
2018-07-16 0:47 ` Phil Reid
2018-07-17 9:09 ` Wolfram Sang [this message]
2018-07-17 9:27 ` Phil Reid
2018-07-24 7:26 ` Wolfram Sang
2018-07-25 3:26 ` Phil Reid
2018-07-13 21:09 ` [PATCH/RFT 2/6] i2c: imx: " Wolfram Sang
2018-07-23 12:47 ` Lucas Stach
2018-07-24 7:28 ` Wolfram Sang
2018-07-24 13:01 ` Wolfram Sang
2018-07-13 21:09 ` [PATCH/RFT 3/6] i2c: designware: set SDA as output for recovery Wolfram Sang
2018-07-13 21:09 ` [PATCH/RFT 4/6] i2c: davinci: " Wolfram Sang
2018-07-13 21:09 ` [PATCH/RFT 5/6] i2c: imx: " Wolfram Sang
2018-07-13 21:09 ` [PATCH/RFT 6/6] i2c: recovery: remove bogus check if SDA GPIO is set to output Wolfram Sang
2018-07-16 9:29 ` Ulrich Hecht
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