From: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
To: Stephan Gerhold <stephan@gerhold.net>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>
Cc: Rob Herring <robh+dt@kernel.org>,
linux-nfc@lists.01.org, netdev@vger.kernel.org,
devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
Bongsu Jeon <bongsu.jeon@samsung.com>,
~postmarketos/upstreaming@lists.sr.ht
Subject: [linux-nfc] Re: [PATCH v2 2/2] nfc: s3fwrn5: i2c: Enable optional clock from device tree
Date: Wed, 19 May 2021 12:13:05 -0400 [thread overview]
Message-ID: <86461091-617b-62ec-a9e5-2aec337d69ce@canonical.com> (raw)
In-Reply-To: <20210519091613.7343-2-stephan@gerhold.net>
On 19/05/2021 05:16, Stephan Gerhold wrote:
> S3FWRN5 depends on a clock input ("XI" pin) to function properly.
> Depending on the hardware configuration this could be an always-on
> oscillator or some external clock that must be explicitly enabled.
>
> So far we assumed that the clock is always-on.
> Make the driver request an (optional) clock from the device tree
> and make sure the clock is running before starting S3FWRN5.
>
> Note: S3FWRN5 asserts "GPIO2" whenever it needs the clock input to
> function correctly. On some hardware configurations, GPIO2 is
> connected directly to an input pin of the external clock provider
> (e.g. the main PMIC of the SoC). In that case, it can automatically
> AND the clock enable bit and clock request from S3FWRN5 so that
> the clock is actually only enabled when needed.
>
> It is also conceivable that on some other hardware configuration
> S3FWRN5's GPIO2 might be connected as a regular GPIO input
> of the SoC. In that case, follow-up patches could extend the
> driver to request the GPIO, set up an interrupt and only enable
> the clock when requested by S3FWRN5.
>
> Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
> ---
> This allows NFC to work properly on the Samsung Galaxy A3/A5 (2015).
>
> Changes in v2: Rewrite commit message and comment based on discussion
>
> Note: I tried to explain the setup a bit better but dropped most of
> the explanations about the exact configuration on the Samsung
> Galaxy A5. I think the HW-specific details were more confusing
> than helping. :)
>
> v1: https://lore.kernel.org/netdev/20210518133935.571298-2-stephan@gerhold.net/
> ---
> drivers/nfc/s3fwrn5/i2c.c | 30 ++++++++++++++++++++++++++++--
> 1 file changed, 28 insertions(+), 2 deletions(-)
>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Best regards,
Krzysztof
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next prev parent reply other threads:[~2021-05-19 16:13 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-19 9:16 [linux-nfc] [PATCH v2 1/2] dt-bindings: net: nfc: s3fwrn5: Add optional clock Stephan Gerhold
2021-05-19 9:16 ` [linux-nfc] [PATCH v2 2/2] nfc: s3fwrn5: i2c: Enable optional clock from device tree Stephan Gerhold
2021-05-19 16:13 ` Krzysztof Kozlowski [this message]
2021-05-19 15:59 ` [linux-nfc] Re: [PATCH v2 1/2] dt-bindings: net: nfc: s3fwrn5: Add optional clock Krzysztof Kozlowski
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