linux-kernel - Re: [PATCH v3 2/5] mtd: spi-nor: cadence-quadspi: add a delay in write sequence

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Date:   Sun, 24 Sep 2017 18:03:51 +0530
From:   Vignesh R <vigneshr@...com>
To:     Marek Vasut <marek.vasut@...il.com>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>
CC:     David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Rob Herring <robh+dt@...nel.org>,
        <linux-mtd@...ts.infradead.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 2/5] mtd: spi-nor: cadence-quadspi: add a delay in
 write sequence



On 9/24/2017 5:29 PM, Marek Vasut wrote:
> On 09/24/2017 12:59 PM, Vignesh R wrote:
>> As per 66AK2G02 TRM[1] SPRUHY8F section 11.15.5.3 Indirect Access
>> Controller programming sequence, a delay equal to couple of QSPI master
>> clock(~5ns) is required after setting CQSPI_REG_INDIRECTWR_START bit and
>> writing data to the flash. Introduce a quirk flag CQSPI_NEEDS_WR_DELAY
>> to handle this and set this flag for TI 66AK2G SoC.
>>
>> [1]http://www.ti.com/lit/ug/spruhy8f/spruhy8f.pdf
>>
>> Signed-off-by: Vignesh R <vigneshr@...com>
> 
> Is this TI specific or is this controller property ? I wouldn't be
> surprised of the later ...

I am not sure, there is no generic public documentation by cadence for
this IP. TI TRM clearly states this delay is required and I have
verified it practically that this delay is indeed needed.
But current user of this IP, socfpga does not seem to mention anything
about it. So, I guess its TI specific quirk.

> 
>> ---
>>
>> v3:
>> Fix build warnings reported by kbuild test bot.
>>
>>  drivers/mtd/spi-nor/cadence-quadspi.c | 27 ++++++++++++++++++++++++++-
>>  1 file changed, 26 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/mtd/spi-nor/cadence-quadspi.c b/drivers/mtd/spi-nor/cadence-quadspi.c
>> index 53c7d8e0327a..5cd5d6f7303f 100644
>> --- a/drivers/mtd/spi-nor/cadence-quadspi.c
>> +++ b/drivers/mtd/spi-nor/cadence-quadspi.c
>> @@ -38,6 +38,9 @@
>>  #define CQSPI_NAME			"cadence-qspi"
>>  #define CQSPI_MAX_CHIPSELECT		16
>>  
>> +/* Quirks */
>> +#define CQSPI_NEEDS_WR_DELAY		BIT(0)
>> +
>>  struct cqspi_st;
>>  
>>  struct cqspi_flash_pdata {
>> @@ -76,6 +79,7 @@ struct cqspi_st {
>>  	u32			fifo_depth;
>>  	u32			fifo_width;
>>  	u32			trigger_address;
>> +	u32			wr_delay;
>>  	struct cqspi_flash_pdata f_pdata[CQSPI_MAX_CHIPSELECT];
>>  };
>>  
>> @@ -608,6 +612,15 @@ static int cqspi_indirect_write_execute(struct spi_nor *nor,
>>  	reinit_completion(&cqspi->transfer_complete);
>>  	writel(CQSPI_REG_INDIRECTWR_START_MASK,
>>  	       reg_base + CQSPI_REG_INDIRECTWR);
>> +	/*
>> +	 * As per 66AK2G02 TRM SPRUHY8F section 11.15.5.3 Indirect Access
>> +	 * Controller programming sequence, couple of cycles of
>> +	 * QSPI_REF_CLK delay is required for the above bit to
>> +	 * be internally synchronized by the QSPI module. Provide 5
>> +	 * cycles of delay.
>> +	 */
>> +	if (cqspi->wr_delay)
>> +		ndelay(cqspi->wr_delay);
>>  
>>  	while (remaining > 0) {
>>  		write_bytes = remaining > page_size ? page_size : remaining;
>> @@ -1156,6 +1169,7 @@ static int cqspi_probe(struct platform_device *pdev)
>>  	struct cqspi_st *cqspi;
>>  	struct resource *res;
>>  	struct resource *res_ahb;
>> +	unsigned long data;
>>  	int ret;
>>  	int irq;
>>  
>> @@ -1213,6 +1227,10 @@ static int cqspi_probe(struct platform_device *pdev)
>>  	}
>>  
>>  	cqspi->master_ref_clk_hz = clk_get_rate(cqspi->clk);
>> +	data  = (unsigned long)of_device_get_match_data(dev);
>> +	if (data & CQSPI_NEEDS_WR_DELAY)
>> +		cqspi->wr_delay = 5 * DIV_ROUND_UP(NSEC_PER_SEC,
>> +						   cqspi->master_ref_clk_hz);
>>  
>>  	ret = devm_request_irq(dev, irq, cqspi_irq_handler, 0,
>>  			       pdev->name, cqspi);
>> @@ -1284,7 +1302,14 @@ static const struct dev_pm_ops cqspi__dev_pm_ops = {
>>  #endif
>>  
>>  static const struct of_device_id cqspi_dt_ids[] = {
>> -	{.compatible = "cdns,qspi-nor",},
>> +	{
>> +		.compatible = "cdns,qspi-nor",
>> +		.data = (void *)0,
>> +	},
>> +	{
>> +		.compatible = "ti,k2g-qspi",
>> +		.data = (void *)CQSPI_NEEDS_WR_DELAY,
>> +	},
>>  	{ /* end of table */ }
>>  };
>>  
>>
> 
>