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

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Message-ID: <b6e729ee-d63d-4167-925d-f3ec5e49ae75@linaro.org>
Date:   Fri, 15 Sep 2023 14:48:51 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Can Guo <quic_cang@...cinc.com>, 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

On 11.09.2023 12:02, Can Guo wrote:
> 
> On 9/11/2023 5:46 PM, Konrad Dybcio wrote:
>> On 11.09.2023 11:42, Can Guo wrote:
>>> 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.
>> First of all, your email client seems to be inserting 2 newlines
>> instead of 1. If you're using thunderbird, you may want to edit:
>>
>> mail.identity.(default or your mail identity idx).default.compose_html
>>
>> to `false`
>>
>> and add that to your internal wiki page, as I see many @quic folks having
>> this issue.
>>
>>
>> Going back to the main topic, I don't think we understood each other.
>> The commit message states:
>>
>>
>> "Retrieve UFS device version from UFS host controller's spare register
>> which is populated by bootloader"
>>
>>
>> Which means the bootloader is able to somehow determine the value
>> that's in the spare register and write it there.
>>
>> I'm asking whether we can take the logic behind this value and
>> move it to Linux so that we don't depend on the bootloader to
>> guarantee it (e.g. Chrome or some other devices with more exotic
>> fw may not work this way).
>>
>>
>> Konrad
> 
> 
> There is no logic behind this value at all in bootloader, as I explained, after bootloader
> 
> initializes UFS, bootloader simply reads UFS's device version (the value you are referring)
> 
> and write it to the register. But in Linux kernel, we need (or want to know) this value
> 
> BEFORE we initialize UFS host controller (and UFS device).
Can't you just initialize the PHY at G4 or G5 unconditionally,
read back the required info and then decide based on that?

Konrad