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Subject[PATCH net-next v2 2/4] dmaengine: qcom: bam_dma: Add "powered remotely" mode
Date
In some configurations, the BAM DMA controller is set up by a remote
processor and the local processor can simply start making use of it
without setting up the BAM. This is already supported using the
"qcom,controlled-remotely" property.

However, for some reason another possible configuration is that the
remote processor is responsible for powering up the BAM, but we are
still responsible for initializing it (e.g. resetting it etc).

This configuration is quite challenging to handle properly because
the power control is handled through separate channels
(e.g. device-specific SMSM interrupts / smem-states). Great care
must be taken to ensure the BAM registers are not accessed while
the BAM is powered off since this results in a bus stall.

Attempt to support this configuration with minimal device-specific
code in the bam_dma driver by tracking the number of requested
channels. Consumers of DMA channels are responsible to only request
DMA channels when the BAM was powered on by the remote processor,
and to release them before the BAM is powered off.

When the first channel is requested the BAM is initialized (reset)
and it is also put into reset when the last channel was released.

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
---
Changes since RFC:
- Drop qcom-specific terminology "power collapse", instead rename
"qcom,remote-power-collapse" -> "qcom,powered-remotely"

NOTE: This is *not* a compile-time requirement for the BAM-DMUX driver
so this could also go through the dmaengine tree.

See original RFC for a discussion of alternative approaches to handle
this configuration:
https://lore.kernel.org/netdev/20210719145317.79692-3-stephan@gerhold.net/
---
drivers/dma/qcom/bam_dma.c | 88 ++++++++++++++++++++++++--------------
1 file changed, 56 insertions(+), 32 deletions(-)

diff --git a/drivers/dma/qcom/bam_dma.c b/drivers/dma/qcom/bam_dma.c
index c8a77b428b52..1b33a3ebbfec 100644
--- a/drivers/dma/qcom/bam_dma.c
+++ b/drivers/dma/qcom/bam_dma.c
@@ -388,6 +388,8 @@ struct bam_device {
/* execution environment ID, from DT */
u32 ee;
bool controlled_remotely;
+ bool powered_remotely;
+ u32 active_channels;

const struct reg_offset_data *layout;

@@ -415,6 +417,44 @@ static inline void __iomem *bam_addr(struct bam_device *bdev, u32 pipe,
r.ee_mult * bdev->ee;
}

+/**
+ * bam_reset - reset and initialize BAM registers
+ * @bdev: bam device
+ */
+static void bam_reset(struct bam_device *bdev)
+{
+ u32 val;
+
+ /* s/w reset bam */
+ /* after reset all pipes are disabled and idle */
+ val = readl_relaxed(bam_addr(bdev, 0, BAM_CTRL));
+ val |= BAM_SW_RST;
+ writel_relaxed(val, bam_addr(bdev, 0, BAM_CTRL));
+ val &= ~BAM_SW_RST;
+ writel_relaxed(val, bam_addr(bdev, 0, BAM_CTRL));
+
+ /* make sure previous stores are visible before enabling BAM */
+ wmb();
+
+ /* enable bam */
+ val |= BAM_EN;
+ writel_relaxed(val, bam_addr(bdev, 0, BAM_CTRL));
+
+ /* set descriptor threshhold, start with 4 bytes */
+ writel_relaxed(DEFAULT_CNT_THRSHLD,
+ bam_addr(bdev, 0, BAM_DESC_CNT_TRSHLD));
+
+ /* Enable default set of h/w workarounds, ie all except BAM_FULL_PIPE */
+ writel_relaxed(BAM_CNFG_BITS_DEFAULT, bam_addr(bdev, 0, BAM_CNFG_BITS));
+
+ /* enable irqs for errors */
+ writel_relaxed(BAM_ERROR_EN | BAM_HRESP_ERR_EN,
+ bam_addr(bdev, 0, BAM_IRQ_EN));
+
+ /* unmask global bam interrupt */
+ writel_relaxed(BAM_IRQ_MSK, bam_addr(bdev, 0, BAM_IRQ_SRCS_MSK_EE));
+}
+
/**
* bam_reset_channel - Reset individual BAM DMA channel
* @bchan: bam channel
@@ -512,6 +552,9 @@ static int bam_alloc_chan(struct dma_chan *chan)
return -ENOMEM;
}

+ if (bdev->active_channels++ == 0 && bdev->powered_remotely)
+ bam_reset(bdev);
+
return 0;
}

@@ -565,6 +608,13 @@ static void bam_free_chan(struct dma_chan *chan)
/* disable irq */
writel_relaxed(0, bam_addr(bdev, bchan->id, BAM_P_IRQ_EN));

+ if (--bdev->active_channels == 0 && bdev->powered_remotely) {
+ /* s/w reset bam */
+ val = readl_relaxed(bam_addr(bdev, 0, BAM_CTRL));
+ val |= BAM_SW_RST;
+ writel_relaxed(val, bam_addr(bdev, 0, BAM_CTRL));
+ }
+
err:
pm_runtime_mark_last_busy(bdev->dev);
pm_runtime_put_autosuspend(bdev->dev);
@@ -1164,38 +1214,10 @@ static int bam_init(struct bam_device *bdev)
bdev->num_channels = val & BAM_NUM_PIPES_MASK;
}

- if (bdev->controlled_remotely)
+ if (bdev->controlled_remotely || bdev->powered_remotely)
return 0;

- /* s/w reset bam */
- /* after reset all pipes are disabled and idle */
- val = readl_relaxed(bam_addr(bdev, 0, BAM_CTRL));
- val |= BAM_SW_RST;
- writel_relaxed(val, bam_addr(bdev, 0, BAM_CTRL));
- val &= ~BAM_SW_RST;
- writel_relaxed(val, bam_addr(bdev, 0, BAM_CTRL));
-
- /* make sure previous stores are visible before enabling BAM */
- wmb();
-
- /* enable bam */
- val |= BAM_EN;
- writel_relaxed(val, bam_addr(bdev, 0, BAM_CTRL));
-
- /* set descriptor threshhold, start with 4 bytes */
- writel_relaxed(DEFAULT_CNT_THRSHLD,
- bam_addr(bdev, 0, BAM_DESC_CNT_TRSHLD));
-
- /* Enable default set of h/w workarounds, ie all except BAM_FULL_PIPE */
- writel_relaxed(BAM_CNFG_BITS_DEFAULT, bam_addr(bdev, 0, BAM_CNFG_BITS));
-
- /* enable irqs for errors */
- writel_relaxed(BAM_ERROR_EN | BAM_HRESP_ERR_EN,
- bam_addr(bdev, 0, BAM_IRQ_EN));
-
- /* unmask global bam interrupt */
- writel_relaxed(BAM_IRQ_MSK, bam_addr(bdev, 0, BAM_IRQ_SRCS_MSK_EE));
-
+ bam_reset(bdev);
return 0;
}

@@ -1257,8 +1279,10 @@ static int bam_dma_probe(struct platform_device *pdev)

bdev->controlled_remotely = of_property_read_bool(pdev->dev.of_node,
"qcom,controlled-remotely");
+ bdev->powered_remotely = of_property_read_bool(pdev->dev.of_node,
+ "qcom,powered-remotely");

- if (bdev->controlled_remotely) {
+ if (bdev->controlled_remotely || bdev->powered_remotely) {
ret = of_property_read_u32(pdev->dev.of_node, "num-channels",
&bdev->num_channels);
if (ret)
@@ -1270,7 +1294,7 @@ static int bam_dma_probe(struct platform_device *pdev)
dev_err(bdev->dev, "num-ees unspecified in dt\n");
}

- if (bdev->controlled_remotely)
+ if (bdev->controlled_remotely || bdev->powered_remotely)
bdev->bamclk = devm_clk_get_optional(bdev->dev, "bam_clk");
else
bdev->bamclk = devm_clk_get(bdev->dev, "bam_clk");
--
2.33.0
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