linux-kernel - Re: [PATCH 2/6] scsi: ufs: ufs-qcom: Add support for UFS device version detection

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Date:   Mon, 11 Sep 2023 17:42:06 +0800
From:   Can Guo <quic_cang@...cinc.com>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>, <mani@...nel.org>,
        <quic_nguyenb@...cinc.com>, <quic_nitirawa@...cinc.com>,
        <martin.petersen@...cle.com>
CC:     <linux-scsi@...r.kernel.org>, Andy Gross <agross@...nel.org>,
        "Bjorn Andersson" <andersson@...nel.org>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "open list:UNIVERSAL FLASH STORAGE HOST CONTROLLER DRIVER..." 
        <linux-arm-msm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/6] scsi: ufs: ufs-qcom: Add support for UFS device
 version detection

Hi Konrad,

On 9/11/2023 5:17 PM, Konrad Dybcio wrote:
> On 11.09.2023 07:59, Can Guo wrote:
>> From: "Bao D. Nguyen" <quic_nguyenb@...cinc.com>
>>
>> Retrieve UFS device version from UFS host controller's spare register
>> which is populated by bootloader, and use the UFS device version together
>> with host controller's HW version to decide the proper power modes which
>> should be used to configure the UFS PHY.
> That sounds a bit fishy.. is there no bootloader-independent
> solution to that? Can't we bring in the code that the bootloader
> uses to determine these values?
>
> Konrad


Agree, it is.


All these complexities come from one request from PHY design team - 
power saving.

And to achieve power saving, Qualcomm UFS developers are requested to 
use the

lowest hanging PHY settings which can sustain the Max agreed HS Gear 
(btw host

and UFS device) during UFS's lifecycle in High Level OS,  whereas the 
power saving

request does not apply to bootloader, which works for only a few seconds 
during

bootup. Hence, there is no such version detect code in bootloader -  it 
just uses the

highest PHY settings to configure PHY, boot up UFS and put UFS device 
version in this

register.


Thanks,

Can Guo.