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

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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@xxxxxxxxxxx>

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?


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

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).


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 Guo.

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