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[v2] spi: cadence-quadspi: Disable irqs during indirect reads

Message ID 20220813042616.1372110-1-niravkumar.l.rabara@intel.com
State Superseded
Headers show
Series [v2] spi: cadence-quadspi: Disable irqs during indirect reads | expand

Commit Message

niravkumar.l.rabara@intel.com Aug. 13, 2022, 4:26 a.m. UTC 
From: Niravkumar L Rabara <niravkumar.l.rabara@intel.com>

On architecture where reading the SRAM is slower than the pace at
controller fills it, with interrupt enabled while reading from
SRAM FIFO causes unwanted interrupt storm to CPU.

The inner "bytes to read" loop never exits and waits for the completion
so it is enough to only enable the watermark interrupt when we
are out of bytes to read, which only happens when we start the
transfer (waiting for the FIFO to fill up initially) if the SRAM
is slow.

So only using read watermark interrupt, as the current implementation
doesn't utilize the SRAM full and indirect complete read interrupt.
And disable all the read interrupts while reading from SRAM.

Signed-off-by: Niravkumar L Rabara <niravkumar.l.rabara@intel.com>
---
 drivers/spi/spi-cadence-quadspi.c | 38 +++++++++++++++++++++++++++----
 1 file changed, 34 insertions(+), 4 deletions(-)

Comments

Mark Brown Aug. 22, 2022, 3:31 p.m. UTC | #1 
On Sat, 13 Aug 2022 12:26:16 +0800, niravkumar.l.rabara@intel.com wrote:
> From: Niravkumar L Rabara <niravkumar.l.rabara@intel.com>
> 
> On architecture where reading the SRAM is slower than the pace at
> controller fills it, with interrupt enabled while reading from
> SRAM FIFO causes unwanted interrupt storm to CPU.
> 
> The inner "bytes to read" loop never exits and waits for the completion
> so it is enough to only enable the watermark interrupt when we
> are out of bytes to read, which only happens when we start the
> transfer (waiting for the FIFO to fill up initially) if the SRAM
> is slow.
> 
> [...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-next

Thanks!

[1/1] spi: cadence-quadspi: Disable irqs during indirect reads
      commit: 9ee5b6d53b8c99d13a47227e3b7052a1365556c9

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark
diff mbox series

Patch

diff --git a/drivers/spi/spi-cadence-quadspi.c b/drivers/spi/spi-cadence-quadspi.c
index 72b1a5a2298c..e12ab5b43f34 100644
--- a/drivers/spi/spi-cadence-quadspi.c
+++ b/drivers/spi/spi-cadence-quadspi.c
@@ -39,6 +39,7 @@ 
 #define CQSPI_DISABLE_DAC_MODE		BIT(1)
 #define CQSPI_SUPPORT_EXTERNAL_DMA	BIT(2)
 #define CQSPI_NO_SUPPORT_WR_COMPLETION	BIT(3)
+#define CQSPI_SLOW_SRAM		BIT(4)
 
 /* Capabilities */
 #define CQSPI_SUPPORTS_OCTAL		BIT(0)
@@ -87,6 +88,7 @@  struct cqspi_st {
 	bool			use_dma_read;
 	u32			pd_dev_id;
 	bool			wr_completion;
+	bool			slow_sram;
 };
 
 struct cqspi_driver_platdata {
@@ -333,7 +335,10 @@  static irqreturn_t cqspi_irq_handler(int this_irq, void *dev)
 		}
 	}
 
-	irq_status &= CQSPI_IRQ_MASK_RD | CQSPI_IRQ_MASK_WR;
+	else if (!cqspi->slow_sram)
+		irq_status &= CQSPI_IRQ_MASK_RD | CQSPI_IRQ_MASK_WR;
+	else
+		irq_status &= CQSPI_REG_IRQ_WATERMARK | CQSPI_IRQ_MASK_WR;
 
 	if (irq_status)
 		complete(&cqspi->transfer_complete);
@@ -673,7 +678,18 @@  static int cqspi_indirect_read_execute(struct cqspi_flash_pdata *f_pdata,
 	/* Clear all interrupts. */
 	writel(CQSPI_IRQ_STATUS_MASK, reg_base + CQSPI_REG_IRQSTATUS);
 
-	writel(CQSPI_IRQ_MASK_RD, reg_base + CQSPI_REG_IRQMASK);
+	/*
+	 * On SoCFPGA platform reading the SRAM is slow due to
+	 * hardware limitation and causing read interrupt storm to CPU,
+	 * so enabling only watermark interrupt to disable all read
+	 * interrupts later as we want to run "bytes to read" loop with
+	 * all the read interrupts disabled for max performance.
+	 */
+
+	if (!cqspi->slow_sram)
+		writel(CQSPI_IRQ_MASK_RD, reg_base + CQSPI_REG_IRQMASK);
+	else
+		writel(CQSPI_REG_IRQ_WATERMARK, reg_base + CQSPI_REG_IRQMASK);
 
 	reinit_completion(&cqspi->transfer_complete);
 	writel(CQSPI_REG_INDIRECTRD_START_MASK,
@@ -684,6 +700,13 @@  static int cqspi_indirect_read_execute(struct cqspi_flash_pdata *f_pdata,
 						 msecs_to_jiffies(CQSPI_READ_TIMEOUT_MS)))
 			ret = -ETIMEDOUT;
 
+		/*
+		 * Disable all read interrupts until
+		 * we are out of "bytes to read"
+		 */
+		if (cqspi->slow_sram)
+			writel(0x0, reg_base + CQSPI_REG_IRQMASK);
+
 		bytes_to_read = cqspi_get_rd_sram_level(cqspi);
 
 		if (ret && bytes_to_read == 0) {
@@ -715,8 +738,11 @@  static int cqspi_indirect_read_execute(struct cqspi_flash_pdata *f_pdata,
 			bytes_to_read = cqspi_get_rd_sram_level(cqspi);
 		}
 
-		if (remaining > 0)
+		if (remaining > 0) {
 			reinit_completion(&cqspi->transfer_complete);
+			if (cqspi->slow_sram)
+				writel(CQSPI_REG_IRQ_WATERMARK, reg_base + CQSPI_REG_IRQMASK);
+		}
 	}
 
 	/* Check indirect done status */
@@ -1667,6 +1693,8 @@  static int cqspi_probe(struct platform_device *pdev)
 			cqspi->use_dma_read = true;
 		if (ddata->quirks & CQSPI_NO_SUPPORT_WR_COMPLETION)
 			cqspi->wr_completion = false;
+		if (ddata->quirks & CQSPI_SLOW_SRAM)
+			cqspi->slow_sram = true;
 
 		if (of_device_is_compatible(pdev->dev.of_node,
 					    "xlnx,versal-ospi-1.0"))
@@ -1779,7 +1807,9 @@  static const struct cqspi_driver_platdata intel_lgm_qspi = {
 };
 
 static const struct cqspi_driver_platdata socfpga_qspi = {
-	.quirks = CQSPI_DISABLE_DAC_MODE | CQSPI_NO_SUPPORT_WR_COMPLETION,
+	.quirks = CQSPI_DISABLE_DAC_MODE
+			| CQSPI_NO_SUPPORT_WR_COMPLETION
+			| CQSPI_SLOW_SRAM,
 };
 
 static const struct cqspi_driver_platdata versal_ospi = {