archive mirror
 help / color / mirror / Atom feed
From: Krzysztof Kozlowski <>
To: Stephan Gerhold <>,
	"David S. Miller" <>,
	Jakub Kicinski <>
Cc: Rob Herring <>,,,,,
	Bongsu Jeon <>,
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: <> (raw)
In-Reply-To: <>


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 <>
> ---
>  drivers/nfc/s3fwrn5/i2c.c | 32 ++++++++++++++++++++++++++++++--
>  1 file changed, 30 insertions(+), 2 deletions(-)

Best regards,

  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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \ \ \ \
    --cc=~postmarketos/ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).