[05/20] interconnect: qcom: icc-rpm: Introduce keep_alive
Commit Message
The downstream kernel employs the concept of "keeping the bus alive"
by voting for the minimum (XO/19.2MHz) rate at all times on certain
(well, most) buses. This is a very important thing to have, as if we
either have a lackluster/wrong DT that doesn't specify a (high enough)
vote on a certain bus, we may lose access to the entire bus altogether.
This is very apparent when we only start introducing interconnect
support on a given platform and haven't yet introduced voting on all
peripherals.
The same can happen if we only have a single driver casting a vote on
a certain bus and that driver exits/crashes/suspends.
The keepalive vote is limited to the ACTIVE bucket, as keeping a
permanent vote on the SLEEP one could prevent the platform from properly
entering low power mode states.
Introduce the very same concept, with a slight twist: the vendor
kernel checks whether the rate is zero before setting the minimum
vote, but that's rather silly, as in doing so we're at the mercy
of CCF. Instead, explicitly clamp the rates to always be >= 19.2 MHz
for providers with keep_alive=true.
Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
---
drivers/interconnect/qcom/icc-rpm.c | 10 ++++++++++
drivers/interconnect/qcom/icc-rpm.h | 3 +++
2 files changed, 13 insertions(+)
Comments
On 30/05/2023 13:20, Konrad Dybcio wrote:
> The downstream kernel employs the concept of "keeping the bus alive"
> by voting for the minimum (XO/19.2MHz) rate at all times on certain
> (well, most) buses.
> This is a very important thing to have, as if we
> either have a lackluster/wrong DT that doesn't specify a (high enough)
> vote on a certain bus, we may lose access to the entire bus altogether.
> This is very apparent when we only start introducing interconnect
> support on a given platform and haven't yet introduced voting on all
> peripherals.
>
> The same can happen if we only have a single driver casting a vote on
> a certain bus and that driver exits/crashes/suspends.
>
> The keepalive vote is limited to the ACTIVE bucket, as keeping a
> permanent vote on the SLEEP one could prevent the platform from properly
> entering low power mode states.
>
> Introduce the very same concept, with a slight twist: the vendor
> kernel checks whether the rate is zero before setting the minimum
> vote, but that's rather silly, as in doing so we're at the mercy
> of CCF. Instead, explicitly clamp the rates to always be >= 19.2 MHz
> for providers with keep_alive=true.
>
> Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
> ---
> drivers/interconnect/qcom/icc-rpm.c | 10 ++++++++++
> drivers/interconnect/qcom/icc-rpm.h | 3 +++
> 2 files changed, 13 insertions(+)
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
@@ -50,6 +50,8 @@
#define NOC_QOS_MODE_FIXED_VAL 0x0
#define NOC_QOS_MODE_BYPASS_VAL 0x2
+#define ICC_BUS_CLK_MIN_RATE 19200000ULL
+
static int qcom_icc_set_qnoc_qos(struct icc_node *src)
{
struct icc_provider *provider = src->provider;
@@ -380,6 +382,13 @@ static int qcom_icc_set(struct icc_node *src, struct icc_node *dst)
do_div(rate, src_qn->buswidth);
rate = min_t(u64, rate, LONG_MAX);
+ /*
+ * Downstream checks whether the requested rate is zero, but it makes little sense
+ * to vote for a value that's below the lower threshold, so let's not do so.
+ */
+ if (bucket == QCOM_ICC_BUCKET_WAKE && qp->keep_alive)
+ rate = max(ICC_BUS_CLK_MIN_RATE, rate);
+
if (qp->bus_clk_rate[i] == rate)
continue;
@@ -453,6 +462,7 @@ int qnoc_probe(struct platform_device *pdev)
for (i = 0; i < qp->num_bus_clks; i++)
qp->bus_clks[i].id = bus_clocks[i];
+ qp->keep_alive = desc->keep_alive;
qp->type = desc->type;
qp->qos_offset = desc->qos_offset;
@@ -33,6 +33,7 @@ enum qcom_icc_type {
* @bus_clk_rate: bus clock rate in Hz
* @bus_clks: the clk_bulk_data table of bus clocks
* @intf_clks: a clk_bulk_data array of interface clocks
+ * @keep_alive: whether to always keep a minimum vote on the bus clocks
* @is_on: whether the bus is powered on
*/
struct qcom_icc_provider {
@@ -45,6 +46,7 @@ struct qcom_icc_provider {
u64 bus_clk_rate[NUM_BUS_CLKS];
struct clk_bulk_data bus_clks[NUM_BUS_CLKS];
struct clk_bulk_data *intf_clks;
+ bool keep_alive;
bool is_on;
};
@@ -102,6 +104,7 @@ struct qcom_icc_desc {
const char * const *bus_clocks;
const char * const *intf_clocks;
size_t num_intf_clocks;
+ bool keep_alive;
bool no_clk_scaling;
enum qcom_icc_type type;
const struct regmap_config *regmap_cfg;