From: Krzysztof Kozlowski <firstname.lastname@example.org>
To: Stephan Gerhold <email@example.com>,
"David S. Miller" <firstname.lastname@example.org>,
Jakub Kicinski <email@example.com>
Cc: Rob Herring <firstname.lastname@example.org>,
Bongsu Jeon <email@example.com>,
Subject: Re: [linux-nfc] [PATCH 2/2] nfc: s3fwrn5: i2c: Enable optional clock from device tree
Date: Tue, 18 May 2021 10:30:43 -0400 [thread overview]
Message-ID: <firstname.lastname@example.org> (raw)
Thanks for the patch.
On 18/05/2021 09:39, Stephan Gerhold wrote:
> s3fwrn5 has a NFC_CLK_REQ output GPIO, which is asserted whenever
> the clock is needed for the current operation. This GPIO can be either
> connected directly to the clock provider, or must be monitored by
> this driver.
> As an example for the first case, on many Qualcomm devices the
> NFC clock is provided by the main PMIC. The clock can be either
> permanently enabled (clocks = <&rpmcc RPM_SMD_BB_CLK2>) or enabled
> only when requested through a special input pin on the PMIC
> (clocks = <&rpmcc RPM_SMD_BB_CLK2_PIN>).
> On the Samsung Galaxy A3/A5 (2015, Qualcomm MSM8916) this mechanism
> is used with S3FWRN5's NFC_CLK_REQ output GPIO to enable the clock
> only when necessary. However, to make that work the s3fwrn5 driver
> must keep the RPM_SMD_BB_CLK2_PIN clock enabled.
This contradicts the code. You wrote that pin should be kept enabled
(somehow... by driver? by it's firmware?) but your code requests the
clock from provider.
> This commit adds support for this by requesting an optional clock
Don't write "This commit".
> and keeping it permanently enabled. Note that the actual (physical)
> clock won't be permanently enabled since this will depend on the
> output of NFC_CLK_REQ from S3FWRN5.
What pin is that "NFC_CLK_REQ"? I cannot find such name. Is it GPIO2?
What clock are you talking here? The one going to the modem part?
I also don't see here how this clock is going to be automatically
on-off... driver does not perform such. Unless you speak about your
particular HW configuration where the GPIO is somehow connected with AND
(but then it is not relevant to the code).
> In the future (when needed by some other device) this could be
> extended to work for the second case (monitoring the NFC_CLK_REQ
> GPIO and enabling the clock from the kernel when needed).
> Signed-off-by: Stephan Gerhold <email@example.com>
> drivers/nfc/s3fwrn5/i2c.c | 32 ++++++++++++++++++++++++++++++--
> 1 file changed, 30 insertions(+), 2 deletions(-)
next prev parent reply other threads:[~2021-05-18 14:30 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-18 13:39 [PATCH 1/2] dt-bindings: net: nfc: s3fwrn5: Add optional clock Stephan Gerhold
2021-05-18 13:39 ` [PATCH 2/2] nfc: s3fwrn5: i2c: Enable optional clock from device tree Stephan Gerhold
2021-05-18 14:30 ` Krzysztof Kozlowski [this message]
2021-05-18 15:00 ` [linux-nfc] " Stephan Gerhold
2021-05-18 15:25 ` [linux-nfc] " Krzysztof Kozlowski
2021-05-18 15:37 ` Stephan Gerhold
2021-05-19 8:07 ` Stephan Gerhold
2021-05-19 15:58 ` Krzysztof Kozlowski
2021-05-20 7:41 ` Stephan Gerhold
2021-05-20 11:40 ` Bongsu Jeon
2021-05-21 15:02 ` Krzysztof Kozlowski
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