[PATCH] i2c: cadence: Clear HOLD bit before xfer_size register rolls over

[PATCH] i2c: cadence: Clear HOLD bit before xfer_size register rolls over

[Raviteja Narayanam]

On Xilinx zynq SOC if the delay between address register write and
control register write in cdns_mrecv function is more, the xfer size
register rolls over and controller is stuck. This is an IP bug and
is resolved in later versions of IP.

To avoid this scenario, disable the interrupts on the current processor
core between the two register writes and enable them later. This can
help achieve the timing constraint.

Signed-off-by: Raviteja Narayanam <raviteja.narayanam@xilinx.com>
---
 drivers/i2c/busses/i2c-cadence.c | 48 ++++++++++++++++++++++++++++++++++------
 1 file changed, 41 insertions(+), 7 deletions(-)

diff --git a/drivers/i2c/busses/i2c-cadence.c b/drivers/i2c/busses/i2c-cadence.c
index e4b7f2a..81b7c45 100644
--- a/drivers/i2c/busses/i2c-cadence.c
+++ b/drivers/i2c/busses/i2c-cadence.c
@@ -578,6 +578,11 @@ static void cdns_i2c_mrecv(struct cdns_i2c *id)
 {
 	unsigned int ctrl_reg;
 	unsigned int isr_status;
+	unsigned long flags;
+	bool hold_clear = false;
+	bool irq_save = false;
+
+	u32 addr;
 
 	id->p_recv_buf = id->p_msg->buf;
 	id->recv_count = id->p_msg->len;
@@ -618,14 +623,43 @@ static void cdns_i2c_mrecv(struct cdns_i2c *id)
 		cdns_i2c_writereg(id->recv_count, CDNS_I2C_XFER_SIZE_OFFSET);
 	}
 
-	/* Set the slave address in address register - triggers operation */
-	cdns_i2c_writereg(id->p_msg->addr & CDNS_I2C_ADDR_MASK,
-						CDNS_I2C_ADDR_OFFSET);
-	/* Clear the bus hold flag if bytes to receive is less than FIFO size */
+	/* Determine hold_clear based on number of bytes to receive and hold flag */
 	if (!id->bus_hold_flag &&
-		((id->p_msg->flags & I2C_M_RECV_LEN) != I2C_M_RECV_LEN) &&
-		(id->recv_count <= CDNS_I2C_FIFO_DEPTH))
-			cdns_i2c_clear_bus_hold(id);
+	    ((id->p_msg->flags & I2C_M_RECV_LEN) != I2C_M_RECV_LEN) &&
+	    (id->recv_count <= CDNS_I2C_FIFO_DEPTH)) {
+		if (cdns_i2c_readreg(CDNS_I2C_CR_OFFSET) & CDNS_I2C_CR_HOLD) {
+			hold_clear = true;
+			if (id->quirks & CDNS_I2C_BROKEN_HOLD_BIT)
+				irq_save = true;
+		}
+	}
+
+	addr = id->p_msg->addr;
+	addr &= CDNS_I2C_ADDR_MASK;
+
+	if (hold_clear) {
+		ctrl_reg = cdns_i2c_readreg(CDNS_I2C_CR_OFFSET) & ~CDNS_I2C_CR_HOLD;
+		/*
+		 * In case of Xilinx Zynq SOC, clear the HOLD bit before transfer size
+		 * register reaches '0'. This is an IP bug which causes transfer size
+		 * register overflow to 0xFF. To satisfy this timing requirement,
+		 * disable the interrupts on current processor core between register
+		 * writes to slave address register and control register.
+		 */
+		if (irq_save)
+			local_irq_save(flags);
+
+		cdns_i2c_writereg(addr, CDNS_I2C_ADDR_OFFSET);
+		cdns_i2c_writereg(ctrl_reg, CDNS_I2C_CR_OFFSET);
+		/* Read it back to avoid bufferring and make sure write happens */
+		cdns_i2c_readreg(CDNS_I2C_CR_OFFSET);
+
+		if (irq_save)
+			local_irq_restore(flags);
+	} else {
+		cdns_i2c_writereg(addr, CDNS_I2C_ADDR_OFFSET);
+	}
+
 	cdns_i2c_writereg(CDNS_I2C_ENABLED_INTR_MASK, CDNS_I2C_IER_OFFSET);
 }
 
-- 
2.7.4


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Re: [PATCH] i2c: cadence: Clear HOLD bit before xfer_size register rolls over

[Michal Simek]

út 24. 11. 2020 v 8:48 odesílatel Raviteja Narayanam
<raviteja.narayanam@xilinx.com> napsal:
>
> On Xilinx zynq SOC if the delay between address register write and
> control register write in cdns_mrecv function is more, the xfer size
> register rolls over and controller is stuck. This is an IP bug and

and the controller

> is resolved in later versions of IP.
>
> To avoid this scenario, disable the interrupts on the current processor
> core between the two register writes and enable them later. This can
> help achieve the timing constraint.
>
> Signed-off-by: Raviteja Narayanam <raviteja.narayanam@xilinx.com>
> ---
>  drivers/i2c/busses/i2c-cadence.c | 48 ++++++++++++++++++++++++++++++++++------
>  1 file changed, 41 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-cadence.c b/drivers/i2c/busses/i2c-cadence.c
> index e4b7f2a..81b7c45 100644
> --- a/drivers/i2c/busses/i2c-cadence.c
> +++ b/drivers/i2c/busses/i2c-cadence.c
> @@ -578,6 +578,11 @@ static void cdns_i2c_mrecv(struct cdns_i2c *id)
>  {
>         unsigned int ctrl_reg;
>         unsigned int isr_status;
> +       unsigned long flags;
> +       bool hold_clear = false;
> +       bool irq_save = false;
> +
> +       u32 addr;
>
>         id->p_recv_buf = id->p_msg->buf;
>         id->recv_count = id->p_msg->len;
> @@ -618,14 +623,43 @@ static void cdns_i2c_mrecv(struct cdns_i2c *id)
>                 cdns_i2c_writereg(id->recv_count, CDNS_I2C_XFER_SIZE_OFFSET);
>         }
>
> -       /* Set the slave address in address register - triggers operation */
> -       cdns_i2c_writereg(id->p_msg->addr & CDNS_I2C_ADDR_MASK,
> -                                               CDNS_I2C_ADDR_OFFSET);
> -       /* Clear the bus hold flag if bytes to receive is less than FIFO size */
> +       /* Determine hold_clear based on number of bytes to receive and hold flag */
>         if (!id->bus_hold_flag &&
> -               ((id->p_msg->flags & I2C_M_RECV_LEN) != I2C_M_RECV_LEN) &&
> -               (id->recv_count <= CDNS_I2C_FIFO_DEPTH))
> -                       cdns_i2c_clear_bus_hold(id);
> +           ((id->p_msg->flags & I2C_M_RECV_LEN) != I2C_M_RECV_LEN) &&
> +           (id->recv_count <= CDNS_I2C_FIFO_DEPTH)) {
> +               if (cdns_i2c_readreg(CDNS_I2C_CR_OFFSET) & CDNS_I2C_CR_HOLD) {
> +                       hold_clear = true;
> +                       if (id->quirks & CDNS_I2C_BROKEN_HOLD_BIT)
> +                               irq_save = true;
> +               }
> +       }
> +
> +       addr = id->p_msg->addr;
> +       addr &= CDNS_I2C_ADDR_MASK;
> +
> +       if (hold_clear) {
> +               ctrl_reg = cdns_i2c_readreg(CDNS_I2C_CR_OFFSET) & ~CDNS_I2C_CR_HOLD;
> +               /*
> +                * In case of Xilinx Zynq SOC, clear the HOLD bit before transfer size
> +                * register reaches '0'. This is an IP bug which causes transfer size
> +                * register overflow to 0xFF. To satisfy this timing requirement,
> +                * disable the interrupts on current processor core between register
> +                * writes to slave address register and control register.
> +                */
> +               if (irq_save)
> +                       local_irq_save(flags);
> +
> +               cdns_i2c_writereg(addr, CDNS_I2C_ADDR_OFFSET);
> +               cdns_i2c_writereg(ctrl_reg, CDNS_I2C_CR_OFFSET);
> +               /* Read it back to avoid bufferring and make sure write happens */
> +               cdns_i2c_readreg(CDNS_I2C_CR_OFFSET);
> +
> +               if (irq_save)
> +                       local_irq_restore(flags);
> +       } else {
> +               cdns_i2c_writereg(addr, CDNS_I2C_ADDR_OFFSET);
> +       }
> +
>         cdns_i2c_writereg(CDNS_I2C_ENABLED_INTR_MASK, CDNS_I2C_IER_OFFSET);
>  }

Unfortunately we can't do anything with this on the Zynq platform. It
is better than nothing.
ZynqMP is not affected.

Acked-by: Michal Simek <michal.simek@xilinx.com>

Thanks,
Michal

-- 
Michal Simek, Ing. (M.Eng), OpenPGP -> KeyID: FE3D1F91
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel - Xilinx Microblaze
Maintainer of Linux kernel - Xilinx Zynq ARM and ZynqMP ARM64 SoCs
U-Boot custodian - Xilinx Microblaze/Zynq/ZynqMP/Versal SoCs

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Re: [PATCH] i2c: cadence: Clear HOLD bit before xfer_size register rolls over

[Wolfram Sang]

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On Tue, Nov 24, 2020 at 01:16:05PM +0530, Raviteja Narayanam wrote:
> On Xilinx zynq SOC if the delay between address register write and
> control register write in cdns_mrecv function is more, the xfer size
> register rolls over and controller is stuck. This is an IP bug and
> is resolved in later versions of IP.
> 
> To avoid this scenario, disable the interrupts on the current processor
> core between the two register writes and enable them later. This can
> help achieve the timing constraint.
> 
> Signed-off-by: Raviteja Narayanam <raviteja.narayanam@xilinx.com>

Applied to for-next, thanks!


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