From: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
To: rfoss@kernel.org, todor.too@gmail.com,
bryan.odonoghue@linaro.org, agross@kernel.org,
andersson@kernel.org, konrad.dybcio@linaro.org,
mchehab@kernel.org, hverkuil-cisco@xs4all.nl,
laurent.pinchart@ideasonboard.com, sakari.ailus@linux.intel.com,
andrey.konovalov@linaro.org
Cc: linux-media@vger.kernel.org, linux-arm-msm@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: [PATCH v5 17/17] media: qcom: camss: Comment CSID dt_id field
Date: Mon, 11 Sep 2023 14:14:11 +0100 [thread overview]
Message-ID: <20230911131411.196033-18-bryan.odonoghue@linaro.org> (raw)
In-Reply-To: <20230911131411.196033-1-bryan.odonoghue@linaro.org>
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@xs4all.nl/
Add a comment so the next hapless programmer doesn't make this same
mistake.
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
---
drivers/media/platform/qcom/camss/camss-csid-gen2.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/drivers/media/platform/qcom/camss/camss-csid-gen2.c b/drivers/media/platform/qcom/camss/camss-csid-gen2.c
index 6ba2b10326444..cee50fc87e9de 100644
--- a/drivers/media/platform/qcom/camss/camss-csid-gen2.c
+++ b/drivers/media/platform/qcom/camss/camss-csid-gen2.c
@@ -352,6 +352,11 @@ static void __csid_configure_stream(struct csid_device *csid, u8 enable, u8 vc)
phy_sel = csid->phy.csiphy_id;
if (enable) {
+ /*
+ * A value caled 'CID' gets generated internal to CAMSS logic
+ * which is a concatenation of [vc:6 | dt_id:2] hence we reuse
+ * the least significant two bits of the VC to 'stuff' the CID value.
+ */
u8 dt_id = vc;
if (tg->enabled) {
--
2.42.0
next prev parent reply other threads:[~2023-09-11 21:19 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-11 13:13 [PATCH v5 00/17] media: qcom: camss: Add parameter passing to remove several outstanding bugs Bryan O'Donoghue
2023-09-11 13:13 ` [PATCH v5 01/17] media: qcom: camss: Amalgamate struct resource with struct resource_ispif Bryan O'Donoghue
2023-09-11 13:13 ` [PATCH v5 02/17] media: qcom: camss: Rename camss struct resources to camss_subdev_resources Bryan O'Donoghue
2023-09-11 13:13 ` [PATCH v5 03/17] media: qcom: camss: Start to move to module compat matched resources Bryan O'Donoghue
2023-09-11 13:13 ` [PATCH v5 04/17] media: qcom: camss: Pass icc bandwidth table as a platform parameter Bryan O'Donoghue
2023-09-11 13:13 ` [PATCH v5 05/17] media: qcom: camss: Pass remainder of variables as resources Bryan O'Donoghue
2023-09-11 13:14 ` [PATCH v5 06/17] media: qcom: camss: Pass line_num from compat resources Bryan O'Donoghue
2023-09-11 13:14 ` [PATCH v5 07/17] media: qcom: camss: Pass CAMSS subdev callbacks via resource ops pointer Bryan O'Donoghue
2023-09-11 13:14 ` [PATCH v5 08/17] media: qcom: camss: Assign the correct number of RDIs per VFE Bryan O'Donoghue
2023-09-11 13:14 ` [PATCH v5 09/17] media: qcom: camss: Remove special case for VFE get/put Bryan O'Donoghue
2023-09-25 8:34 ` Laurent Pinchart
2023-09-11 13:14 ` [PATCH v5 10/17] media: qcom: camss: Untangle if/else spaghetti in camss Bryan O'Donoghue
2023-09-11 13:14 ` [PATCH v5 11/17] media: qcom: camss: Allow clocks vfeN vfe_liteN or vfe_lite Bryan O'Donoghue
2023-09-25 7:10 ` Hans Verkuil
2023-09-25 11:46 ` Bryan O'Donoghue
2023-09-11 13:14 ` [PATCH v5 12/17] media: qcom: camss: Functionally decompose CSIPHY clock lookups Bryan O'Donoghue
2023-09-11 13:14 ` [PATCH v5 13/17] media: qcom: camss: Fix support for setting CSIPHY clock name csiphyX Bryan O'Donoghue
2023-09-11 13:14 ` [PATCH v5 14/17] media: qcom: camss: Support RDI3 for VFE 17x Bryan O'Donoghue
2023-09-11 13:14 ` [PATCH v5 15/17] media: qcom: camss: Move vfe_disable into a common routine where applicable Bryan O'Donoghue
2023-09-11 13:14 ` [PATCH v5 16/17] media: qcom: camss: Propagate vfe_reset error up the callstack Bryan O'Donoghue
2023-09-11 13:14 ` Bryan O'Donoghue [this message]
2023-09-25 7:11 ` [PATCH v5 17/17] media: qcom: camss: Comment CSID dt_id field Hans Verkuil
2023-09-25 8:14 ` Laurent Pinchart
2023-09-25 14:01 ` Bryan O'Donoghue
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