spi: qcom-geni: Fix cs_change handling on the last transfer

spi: qcom-geni: Fix cs_change handling on the last transfer

TPM TIS SPI probe fails with:

   tpm_tis_spi: probe of spi11.0 failed with error -110

TPM TIS SPI sets cs_change=1 on single-transfer messages to keep CS
asserted across the header, wait-state, and data phases of a transaction.
CS deassertion between these phases violates the TCG SPI flow control
specification.

This bug was introduced by commit b99181cdf9fa ("spi-geni-qcom: remove
manual CS control"), which replaced manual CS control with automatic CS
control via the FRAGMENTATION bit. The FRAGMENTATION bit controls CS
behavior after a transfer: when set to 1, CS remains asserted; when
cleared to 0, CS is deasserted.

The commit correctly sets FRAGMENTATION for non-last transfers with
cs_change=0 to keep CS asserted between chained transfers, but misses the
case where cs_change=1 is set on the last transfer. When cs_change=1 on
the last transfer, the client requests CS to remain asserted after the
message completes, so FRAGMENTATION must be set to 1 in this case as well.

Fix setup_se_xfer() to set FRAGMENTATION when cs_change=1 on the last
transfer.

Also fix the same missing case in setup_gsi_xfer() and correct it to
write 1 instead of the raw bitmask FRAGMENTATION (value 4) to
peripheral.fragmentation. This field is a 1-bit boolean consumed by
gpi_create_spi_tre() via u32_encode_bits(..., TRE_SPI_GO_FRAG). Writing 4
to a 1-bit field causes u32_encode_bits() to mask it to 0, silently
disabling the FRAGMENTATION bit in the GPI TRE regardless of the
cs_change logic.

Fixes: b99181cdf9fa ("spi-geni-qcom: remove manual CS control")
Cc: stable@vger.kernel.org
Reviewed-by: Jonathan Marek <jonathan@marek.ca>
Signed-off-by: Viken Dadhaniya <viken.dadhaniya@oss.qualcomm.com>
Link: https://patch.msgid.link/20260609-fix-spi-fragmentation-bit-logic-v2-1-e18efc255563@oss.qualcomm.com
Signed-off-by: Mark Brown <broonie@kernel.org>