Re: [PATCH 2/2] gpmi-nand: Add ERR007117 protection for nfc_apply_timings

[Han Xu]

On 21/11/02 09:20PM, Christian Eggers wrote:
> gpmi_io clock needs to be gated off when changing the parent/dividers of
> enfc_clk_root (i.MX6Q/i.MX6UL) respectively qspi2_clk_root (i.MX6SX).
> Otherwise this rate change can lead to an unresponsive GPMI core which
> results in DMA timeouts and failed driver probe:
> 
> [    4.072318] gpmi-nand 112000.gpmi-nand: DMA timeout, last DMA
> ...
> [    4.370355] gpmi-nand 112000.gpmi-nand: Chip: 0, Error -110
> ...
> [    4.375988] gpmi-nand 112000.gpmi-nand: Chip: 0, Error -22
> [    4.381524] gpmi-nand 112000.gpmi-nand: Error in ECC-based read: -22
> [    4.387988] gpmi-nand 112000.gpmi-nand: Chip: 0, Error -22
> [    4.393535] gpmi-nand 112000.gpmi-nand: Chip: 0, Error -22
> ...
> 
> Other than stated in i.MX 6 erratum ERR007117, it should be sufficient
> to gate only gpmi_io because all other bch/nand clocks are derived from
> different clock roots.
> 
> The i.MX6 reference manuals state that changing clock muxers can cause
> glitches but are silent about changing dividers. But tests showed that
> these glitches can definitely happen on i.MX6ULL. For i.MX7D/8MM in turn,
> the manual guarantees that no glitches can happen when changing
> dividers.
> 
> Co-developed-by: Stefan Riedmueller <s.riedmueller@xxxxxxxxx>
> Signed-off-by: Stefan Riedmueller <s.riedmueller@xxxxxxxxx>
> Signed-off-by: Christian Eggers <ceggers@xxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
> Changelog:
> -----------
> RFC --> v1
> - added comment about clock divider behavior on the different i.MX series
> - perform clock gating also on i.MX6SX
> - only gate gpmi_io clock. Other GPMI/BCH clocks are not affected when
>   ENFC_CLK_ROOT divides are changes
> - add error checking for clk_set_rate()
> - Cc: stable@xxxxxxxxxxxxxxx
> 
>  drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c | 28 +++++++++++++++++++---
>  1 file changed, 25 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c b/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c
> index a1f7000f033e..6e9f7d80ef8b 100644
> --- a/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c
> +++ b/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c
> @@ -713,14 +713,32 @@ static void gpmi_nfc_compute_timings(struct gpmi_nand_data *this,
>  			      (use_half_period ? BM_GPMI_CTRL1_HALF_PERIOD : 0);
>  }
>  
> -static void gpmi_nfc_apply_timings(struct gpmi_nand_data *this)
> +static int gpmi_nfc_apply_timings(struct gpmi_nand_data *this)
>  {
>  	struct gpmi_nfc_hardware_timing *hw = &this->hw;
>  	struct resources *r = &this->resources;
>  	void __iomem *gpmi_regs = r->gpmi_regs;
>  	unsigned int dll_wait_time_us;
> +	int ret;
> +
> +	/* Clock dividers do NOT guarantee a clean clock signal on its output
> +	 * during the change of the divide factor on i.MX6Q/UL/SX. On i.MX7/8,
> +	 * all clock dividers provide these guarantee.
> +	 */
> +	if (GPMI_IS_MX6Q(this) || GPMI_IS_MX6SX(this))
> +		clk_disable_unprepare(r->clock[0]);
> +
> +	ret = clk_set_rate(r->clock[0], hw->clk_rate);
> +	if (ret) {
> +		dev_err(this->dev, "cannot set clock rate to %lu Hz: %d\n", hw->clk_rate, ret);
> +		return ret;
> +	}
>  
> -	clk_set_rate(r->clock[0], hw->clk_rate);
> +	if (GPMI_IS_MX6Q(this) || GPMI_IS_MX6SX(this)) {
> +		ret = clk_prepare_enable(r->clock[0]);
> +		if (ret)
> +			return ret;
> +	}
>  
>  	writel(hw->timing0, gpmi_regs + HW_GPMI_TIMING0);
>  	writel(hw->timing1, gpmi_regs + HW_GPMI_TIMING1);
> @@ -739,6 +757,8 @@ static void gpmi_nfc_apply_timings(struct gpmi_nand_data *this)
>  
>  	/* Wait for the DLL to settle. */
>  	udelay(dll_wait_time_us);
> +
> +	return 0;
>  }
>  
>  static int gpmi_setup_interface(struct nand_chip *chip, int chipnr,
> @@ -2271,7 +2291,9 @@ static int gpmi_nfc_exec_op(struct nand_chip *chip,
>  	 */
>  	if (this->hw.must_apply_timings) {
>  		this->hw.must_apply_timings = false;
> -		gpmi_nfc_apply_timings(this);
> +		ret = gpmi_nfc_apply_timings(this);
> +		if (ret)
> +			return ret;
>  	}
>  
>  	dev_dbg(this->dev, "%s: %d instructions\n", __func__, op->ninstrs);

Acked-by: Han Xu <han.xu@xxxxxxx>

> -- 
> Christian Eggers
> Embedded software developer
> 
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