Merge patch series "scsi: ufs: Add persistent TX Equalization settings support"

Can Guo <can.guo@oss.qualcomm.com> says:

Hi,

This series is a follow-up to the earlier TX Equalization enablement series:

https://lore.kernel.org/all/20260325152154.1604082-1-can.guo@oss.qualcomm.com

In that cover letter, the "Next" section mentioned adding support for
UFS v5.0 Attributes qTxEQGnSettings and wTxEQGnSettingsExt, and enabling
persistent storage/retrieval of optimal TX Equalization settings. This
2-patch series implements that part.

Motivation
==========

TX EQTR procedure is required to find the optimal TX Equalization settings
for HS Gears (4-6) before changing Power Mode to the target HS Gears.
However, TX EQTR procedure introduces latencies to the first Power Mode
change.

With optimal TX Equalization settings stored in UFS v5.0 Attributes
qTxEQGnSettings and wTxEQGnSettingsExt, host software can reuse known-good
settings and avoid going through the TX EQTR procedure.

Array Attribute Model
=====================

qTxEQGnSettings and wTxEQGnSettingsExt are array-type Attributes. Each
element in an array-type Attribute is selected by an (Index, Selector) pair.

For these two attributes:
- Valid Index range: [0, Max HS Gear - 1]
- Valid Selector range: [0, 1]

This effectively forms a 2-dimensional array. For HS-Gear n, its TX
Equalization settings are stored/retrieved at Index (n - 1). Selector is
configurable via a module parameter so that platforms can choose the
Selector policy that matches their use.

Implementation Overview
=======================

1. Introduce a generic helper for 64-bit query attributes:
   ufshcd_query_attr_qword().

2. Add TX EQ settings persistence flow:
   - Read stored settings from qTxEQGnSettings & wTxEQGnSettingsExt.
   - Decode and populate per-gear TX EQ parameters.
   - Use Bit[15] in wTxEQGnSettingsExt as validity indication.
   - Store trained settings back to these attributes for future reuse.

3. Integrate with existing lifecycle:
   - Retrieve settings during device parameter initialization.
   - Store settings during shutdown.

New Module Parameters
=====================

Three module parameters are added for TX EQ settings persistence control:

 - txeq_setting_sel (default: 0, range: 0..1)
    Selects which selector value is used when reading/writing
    qTxEQGnSettings and wTxEQGnSettingsExt.

 - retrieve_txeq_setting (default: true)
    Enables/disables retrieving stored TX EQ settings from device
    attributes during initialization.

 - store_txeq_setting (default: true)
    Enables/disables storing last trained TX EQ settings into device
    attributes during shutdown.

Testing
=======

Tested on a UFS v5.0 platform:

 - TX Equalization setting store path, settings were correctly encoded
   and stored.

 - TX Equalization setting retrieval path, settings were correctly
   extracted and reused.

 - Full TX EQTR procedure was skipped for a given HS Gear when valid
   TX EQ settings
  were provided in qTxEQGnSettings & wTxEQGnSettingsExt for the given HS-Gear.

Link: https://patch.msgid.link/20260424151420.111675-1-can.guo@oss.qualcomm.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>