linux-kernel - Re: [PATCH RFC 1/3] scsi: ufs: set the device reference clock setting

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Date:   Wed, 23 May 2018 13:48:30 -0500
From:   Rob Herring <robh@...nel.org>
To:     Sayali Lokhande <sayalil@...eaurora.org>
Cc:     subhashj@...eaurora.org, cang@...eaurora.org,
        vivek.gautam@...eaurora.org, rnayak@...eaurora.org,
        vinholikatti@...il.com, jejb@...ux.vnet.ibm.com,
        martin.petersen@...cle.com, asutoshd@...eaurora.org,
        linux-scsi@...r.kernel.org, Mark Rutland <mark.rutland@....com>,
        Mathieu Malaterre <malat@...ian.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 1/3] scsi: ufs: set the device reference clock setting

On Tue, May 22, 2018 at 09:51:38AM +0530, Sayali Lokhande wrote:
> From: Subhash Jadavani <subhashj@...eaurora.org>
> 
> UFS host supplies the reference clock to UFS device and UFS device
> specification allows host to provide one of the 4 frequencies (19.2 MHz,
> 26 MHz, 38.4 MHz, 52 MHz) for reference clock. Host should set the
> device reference clock frequency setting in the device based on what
> frequency it is supplying to UFS device.
> 
> Signed-off-by: Subhash Jadavani <subhashj@...eaurora.org>
> [cang@...eaurora.org: Resolved trivial merge conflicts]
> Signed-off-by: Can Guo <cang@...eaurora.org>
> Signed-off-by: Sayali Lokhande <sayalil@...eaurora.org>
> ---
>  .../devicetree/bindings/ufs/ufshcd-pltfrm.txt      |  8 +++
>  drivers/scsi/ufs/ufs.h                             |  9 ++++
>  drivers/scsi/ufs/ufshcd-pltfrm.c                   | 20 ++++++++
>  drivers/scsi/ufs/ufshcd.c                          | 60 ++++++++++++++++++++++
>  drivers/scsi/ufs/ufshcd.h                          |  2 +
>  5 files changed, 99 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt b/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt
> index c39dfef..ac94220 100644
> --- a/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt
> +++ b/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt
> @@ -41,6 +41,12 @@ Optional properties:
>  -lanes-per-direction	: number of lanes available per direction - either 1 or 2.
>  			  Note that it is assume same number of lanes is used both
>  			  directions at once. If not specified, default is 2 lanes per direction.
> +- dev-ref-clk-freq	: Specify the device reference clock frequency, must be one of the following:
> +			  0: 19.2 MHz
> +			  1: 26 MHz
> +			  2: 38.4 MHz
> +			  3: 52 MHz
> +			  Defaults to 26 MHz if not specified.

You already have "ref_clk", can't you just read its frequency?

Rob