6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Bryan O'Donoghue bryan.odonoghue@linaro.org
commit f910d3ba78a2677c23508f225eb047d89eb4b2b6 upstream.
Digging into the documentation we find that the DT_ID bitfield is used to map the six bit DT to a two bit ID code. This value is concatenated to the VC bitfield to create a CID value. DT_ID is the two least significant bits of CID and VC the most significant bits.
Originally we set dt_id = vc * 4 in and then subsequently set dt_id = vc.
commit 3c4ed72a16bc ("media: camss: sm8250: Virtual channels for CSID") silently fixed the multiplication by four which would give a better value for the generated CID without mentioning what was being done or why.
Next up I haplessly changed the value back to "dt_id = vc * 4" since there didn't appear to be any logic behind it.
Hans asked what the change was for and I honestly couldn't remember the provenance of it, so I dug in.
Link: https://lore.kernel.org/linux-arm-msm/edd4bf9b-0e1b-883c-1a4d-50f4102c3924@x...
Add a comment so the next hapless programmer doesn't make this same mistake.
Signed-off-by: Bryan O'Donoghue bryan.odonoghue@linaro.org Signed-off-by: Hans Verkuil hverkuil-cisco@xs4all.nl Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/media/platform/qcom/camss/camss-csid-gen2.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-)
--- a/drivers/media/platform/qcom/camss/camss-csid-gen2.c +++ b/drivers/media/platform/qcom/camss/camss-csid-gen2.c @@ -352,7 +352,19 @@ static void __csid_configure_stream(stru phy_sel = csid->phy.csiphy_id;
if (enable) { - u8 dt_id = vc; + /* + * DT_ID is a two bit bitfield that is concatenated with + * the four least significant bits of the five bit VC + * bitfield to generate an internal CID value. + * + * CSID_RDI_CFG0(vc) + * DT_ID : 28:27 + * VC : 26:22 + * DT : 21:16 + * + * CID : VC 3:0 << 2 | DT_ID 1:0 + */ + u8 dt_id = vc & 0x03;
if (tg->enabled) { /* configure one DT, infinite frames */