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

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Date:   Fri, 25 May 2018 17:50:40 +0530
From:   "sayali" <sayalil@...eaurora.org>
To:     "'Rob Herring'" <robh@...nel.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

Hi Rob,

For UFS provisioning, all we need is ref_clk to be set to 19.2MHz before
actual descriptor write happens.
So I can actually avoid parsing it via DT and use REF_CLK_FREQ_19_2_MHZ from
enum ref_clk_freq (which is already added in my current implementation).

Thanks,
Sayali
-----Original Message-----
From: Rob Herring [mailto:robh@...nel.org] 
Sent: Thursday, May 24, 2018 12:19 AM
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