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SubjectRE: [PATCH V2 1/3] scsi: ufs: set the device reference clock setting
Date
Hi Rob,

Please check my comment inline.

Thanks,
Sayali
-----Original Message-----
From: Rob Herring [mailto:robh@kernel.org]
Sent: Thursday, June 14, 2018 7:59 PM
To: sayali <sayalil@codeaurora.org>
Cc: Subhash Jadavani <subhashj@codeaurora.org>; Can Guo <cang@codeaurora.org>; Vivek Gautam <vivek.gautam@codeaurora.org>; Rajendra Nayak <rnayak@codeaurora.org>; Vinayak Holikatti <vinholikatti@gmail.com>; James E.J. Bottomley <jejb@linux.vnet.ibm.com>; Martin K. Petersen <martin.petersen@oracle.com>; asutoshd@codeaurora.org; Evan Green <evgreen@chromium.org>; linux-scsi@vger.kernel.org; Mark Rutland <mark.rutland@arm.com>; Mathieu Malaterre <malat@debian.org>; open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS <devicetree@vger.kernel.org>; open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH V2 1/3] scsi: ufs: set the device reference clock setting

On Thu, Jun 14, 2018 at 5:33 AM, sayali <sayalil@codeaurora.org> wrote:
> Comment inline.
>
> Thanks,
> Sayali
> -----Original Message-----
> From: Rob Herring [mailto:robh@kernel.org]
> Sent: Wednesday, June 13, 2018 12:57 AM
> To: Sayali Lokhande <sayalil@codeaurora.org>
> Cc: subhashj@codeaurora.org; cang@codeaurora.org;
> vivek.gautam@codeaurora.org; rnayak@codeaurora.org;
> vinholikatti@gmail.com; jejb@linux.vnet.ibm.com;
> martin.petersen@oracle.com; asutoshd@codeaurora.org;
> evgreen@chromium.org; linux-scsi@vger.kernel.org; Mark Rutland
> <mark.rutland@arm.com>; Mathieu Malaterre <malat@debian.org>; open
> list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS
> <devicetree@vger.kernel.org>; open list <linux-kernel@vger.kernel.org>
> Subject: Re: [PATCH V2 1/3] scsi: ufs: set the device reference clock
> setting
>
> On Fri, Jun 08, 2018 at 04:36:28PM +0530, Sayali Lokhande wrote:
>> From: Subhash Jadavani <subhashj@codeaurora.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@codeaurora.org>
>> Signed-off-by: Can Guo <cang@codeaurora.org>
>> Signed-off-by: Sayali Lokhande <sayalil@codeaurora.org>
>> ---
>> .../devicetree/bindings/ufs/ufshcd-pltfrm.txt | 7 +++
>> drivers/scsi/ufs/ufs.h | 9 ++++
>> drivers/scsi/ufs/ufshcd-pltfrm.c | 24 ++++++++++
>> drivers/scsi/ufs/ufshcd.c | 52
> ++++++++++++++++++++++
>> drivers/scsi/ufs/ufshcd.h | 1 +
>> 5 files changed, 93 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt
>> b/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt
>> index c39dfef..4522434 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.
>
> I must have misunderstood your last response. I thought you could
> handle things without DT. If not, my question remains.
> [Sayali]: Ref clk frequency setting could vary from
> platfrom-to-platform(vendor specific). Hence we need to pass it via DT.
> Currently in DT we do not set/mention any ref clk frequency
> parameter. Hence I have added one new DT entry to configure
> required ref clk freq.

The clocks property contains "ref_clk". Is that not the same clock?
Why can't you read what that frequency is? Or you need to be able to change it to a specific frequency? These all look like typical oscillator frequencies, so I wouldn't expect you could change them (other than divide by 2 maybe).
[Sayali] : It is the same "ref_clk", but we need to be able to change it to a specific frequency as per requirement. Thus, we need new DT entry to specify/override reference clock frequency as per need.

Rob

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