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

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Message-ID: <159796935923.334488.7479152222902825306@swboyd.mtv.corp.google.com>
Date:   Thu, 20 Aug 2020 17:22:39 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Roja Rani Yarubandi <rojay@...eaurora.org>, wsa@...nel.org
Cc:     dianders@...omium.org, saiprakash.ranjan@...eaurora.org,
        gregkh@...uxfoundation.org, mka@...omium.org,
        akashast@...eaurora.org, msavaliy@....qualcomm.com,
        skakit@...eaurora.org, rnayak@...eaurora.org, agross@...nel.org,
        bjorn.andersson@...aro.org, linux-arm-msm@...r.kernel.org,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        sumit.semwal@...aro.org, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
        Roja Rani Yarubandi <rojay@...eaurora.org>
Subject: Re: [PATCH V2 2/2] i2c: i2c-qcom-geni: Add shutdown callback for i2c

Quoting Roja Rani Yarubandi (2020-08-20 03:35:22)
> 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@...eaurora.org>
> ---

I'd still put a Fixes tag because it's fixing the driver when someone
runs shutdown.

> 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);
> +       }
> +       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);
> +       if (dma)
> +               geni_i2c_stop_xfer(gi2c);

Any reason the if (dma) check isn't inside geni_i2c_stop_xfer()?
Checking for dma and then bailing out early should work and keep the
logic in one function. Then the pm_runtime_sync() call could go in there
too and if (!dma) goto out. This assumes that we're going to call
geni_i2c_stop_xfer() from somewhere else, like if a transfer times out
or something?

> +
> +       pm_runtime_put_sync_suspend(gi2c->se.dev);
> +}
> +
>  static int __maybe_unused geni_i2c_runtime_suspend(struct device *dev)
>  {
>         int ret;