Re: [PATCH v2 2/2] scsi: ufs: Serve the device init reads from one aggregated read

[Stanley Jhu <stanleyjhu@google.com>]

On Wed, 30 Sep 2026 14:18:25 +0900, Hyeoncheol Jeong wrote:
> +	for (i = 0; i < idn; i++)
> +		off += ufs_agg_attr_width[i];

This assumes the Attributes group (Group Type 02h) is serialized by
ascending IDN at fixed offsets. JESD220H Section 10.7.9.14 and
Table 10.56 define only the group header and Next Group Offset chain;
the intra-group layout and ordering are not specified.

How does this handle:

- Array attributes: wContextConf (10h) requires INDEX=LUN and
  SELECTOR=ContextID, where valid SELECTOR values are 01h..0Fh so 00h
  is invalid (Table 14.28), yet AGGREGATED READ leaves bytes 14-17
  Reserved (Table 10.42). Assuming 2 bytes in ufs_agg_attr_width[]
  breaks if a device omits it or returns all elements.

- Optional attributes: if a device omits unimplemented optional
  attributes such as PSA (15h, 16h) instead of zero-padding them,
  subsequent attributes shift (e.g. bWriteBoosterBufferLifeTimeEst at
  1Eh shifts by 5 bytes) with no per-entry framing to detect it.

- Write-only attributes: ufs_agg_attr_width[] reserves 4 bytes for
  dSecondsPassed (0Fh), which Table 14.28 marks Write only. Whether a
  device serializes write-only attributes in a read response is
  unspecified.

> +	if (index == 0 && !ufshcd_agg_attr(hba, idn, out))
> +		return 0;

The commit message states that bWriteBoosterBufferLifeTimeEst is
served from the packet only in shared-buffer mode. In LU-dedicated
mode (bWriteBoosterBufferType != 01h, Table 14.28 NOTE 15) with
wb_dedicated_lu == 0, ufshcd_wb_get_query_index() also returns 0, so
this check serves LU 0's lifetime from a packet with no LUN qualifier.

> +	if (!group_buf || idn >= group_len)
> +		return -ENOENT;
> +
> +	*out = group_buf[idn];

The Flags group (Group Type 01h) has the same issue: Table 14.26
NOTE 1 distinguishes device-level flags from array flags addressed by
INDEX and SELECTOR, and the specification defines no 1-byte-per-IDN
packed layout.