Re: [PATCH V2 2/2] i2c: i2c-qcom-geni: Add shutdown callback for i2c

[Akash Asthana <akashast@codeaurora.org>]

Hi Roja,

On 8/20/2020 4:05 PM, Roja Rani Yarubandi wrote:
> If the hardware is still accessing memory after SMMU translation
> is disabled (as part of smmu shutdown callback), then the
> IOVAs (I/O virtual address) which it was using will go on the bus
> as the physical addresses which will result in unknown crashes
> like NoC/interconnect errors.
>
> So, implement shutdown callback to i2c driver to unmap DMA mappings
> during system "reboot" or "shutdown".
>
> Signed-off-by: Roja Rani Yarubandi <rojay@codeaurora.org>
> ---
> Changes in V2:
>   - As per Stephen's comments added seperate function for stop transfer,
>     fixed minor nitpicks.
>
>   drivers/i2c/busses/i2c-qcom-geni.c | 43 ++++++++++++++++++++++++++++++
>   include/linux/qcom-geni-se.h       |  5 ++++
>   2 files changed, 48 insertions(+)
>
> diff --git a/drivers/i2c/busses/i2c-qcom-geni.c b/drivers/i2c/busses/i2c-qcom-geni.c
> index 1fda5c7c2cfc..d07f2f33bb75 100644
> --- a/drivers/i2c/busses/i2c-qcom-geni.c
> +++ b/drivers/i2c/busses/i2c-qcom-geni.c
> @@ -486,6 +486,28 @@ static int geni_i2c_xfer(struct i2c_adapter *adap,
>   	return ret;
>   }
>   
> +static void geni_i2c_stop_xfer(struct geni_i2c_dev *gi2c)
> +{
> +	u32 val;
> +	struct geni_se *se = &gi2c->se;
> +
> +	val = readl_relaxed(gi2c->se.base + SE_DMA_DEBUG_REG0);
> +	if (val & DMA_TX_ACTIVE) {
> +		geni_i2c_abort_xfer(gi2c);
> +		gi2c->cur_wr = 0;
> +		if (gi2c->err)
> +			geni_i2c_tx_fsm_rst(gi2c);
> +		geni_se_tx_dma_unprep(se, gi2c->tx_dma, gi2c->xfer_len);
> +	}
should be 'else if', because TX and RX can't happen parallel.
> +	if (val & DMA_RX_ACTIVE) {
> +		geni_i2c_abort_xfer(gi2c);
> +		gi2c->cur_rd = 0;
> +		if (gi2c->err)
> +			geni_i2c_rx_fsm_rst(gi2c);
> +		geni_se_rx_dma_unprep(se, gi2c->rx_dma, gi2c->xfer_len);
> +	}
> +}
> +
>   static u32 geni_i2c_func(struct i2c_adapter *adap)
>   {
>   	return I2C_FUNC_I2C | (I2C_FUNC_SMBUS_EMUL & ~I2C_FUNC_SMBUS_QUICK);
> @@ -617,6 +639,26 @@ static int geni_i2c_remove(struct platform_device *pdev)
>   	return 0;
>   }
>   
> +static void geni_i2c_shutdown(struct platform_device *pdev)
> +{
> +	int ret;
> +	u32 dma;
> +	struct geni_i2c_dev *gi2c = platform_get_drvdata(pdev);
> +	struct geni_se *se = &gi2c->se;
> +
> +	ret = pm_runtime_get_sync(gi2c->se.dev);
> +	if (ret < 0) {
> +		dev_err(gi2c->se.dev, "Failed to resume device: %d\n", ret);
> +		return;
> +	}
> +
> +	dma = readl_relaxed(se->base + SE_GENI_DMA_MODE_EN);

Wrt to current issue context it may be suffice to stop just DMA mode 
transfers but why not stop all mode of active transfer during shutdown 
in a generic way.

Regards,

Akash

> +	if (dma)
> +		geni_i2c_stop_xfer(gi2c);
> +
> +	pm_runtime_put_sync_suspend(gi2c->se.dev);
> +}
> +
>   static int __maybe_unused geni_i2c_runtime_suspend(struct device *dev)
>   {
>   	int ret;
> @@ -677,6 +719,7 @@ MODULE_DEVICE_TABLE(of, geni_i2c_dt_match);
>   static struct platform_driver geni_i2c_driver = {
>   	.probe  = geni_i2c_probe,
>   	.remove = geni_i2c_remove,
> +	.shutdown = geni_i2c_shutdown,
>   	.driver = {
>   		.name = "geni_i2c",
>   		.pm = &geni_i2c_pm_ops,
> diff --git a/include/linux/qcom-geni-se.h b/include/linux/qcom-geni-se.h
> index dd464943f717..c3c016496d98 100644
> --- a/include/linux/qcom-geni-se.h
> +++ b/include/linux/qcom-geni-se.h
> @@ -77,6 +77,7 @@ struct geni_se {
>   #define SE_DMA_RX_FSM_RST		0xd58
>   #define SE_HW_PARAM_0			0xe24
>   #define SE_HW_PARAM_1			0xe28
> +#define SE_DMA_DEBUG_REG0		0xe40
>   
>   /* GENI_FORCE_DEFAULT_REG fields */
>   #define FORCE_DEFAULT	BIT(0)
> @@ -207,6 +208,10 @@ struct geni_se {
>   #define RX_GENI_CANCEL_IRQ		BIT(11)
>   #define RX_GENI_GP_IRQ_EXT		GENMASK(13, 12)
>   
> +/* SE_DMA_DEBUG_REG0 Register fields */
> +#define DMA_TX_ACTIVE			BIT(0)
> +#define DMA_RX_ACTIVE			BIT(1)
> +
>   /* SE_HW_PARAM_0 fields */
>   #define TX_FIFO_WIDTH_MSK		GENMASK(29, 24)
>   #define TX_FIFO_WIDTH_SHFT		24

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