linux-kernel - Re: [PATCH V1 1/1] mtd: mtk-nor: set controller to 4B mode with large capacity flash

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Date:   Fri, 31 Mar 2017 10:56:03 +0200
From:   Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>
To:     Guochun Mao <guochun.mao@...iatek.com>,
        Marek Vasut <marek.vasut@...il.com>
Cc:     Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Mark Rutland <mark.rutland@....com>,
        devicetree@...r.kernel.org, Richard Weinberger <richard@....at>,
        Russell King <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        linux-mtd@...ts.infradead.org,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-mediatek@...ts.infradead.org,
        Cyrille Pitchen <cyrille.pitchen@...el.com>,
        David Woodhouse <dwmw2@...radead.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH V1 1/1] mtd: mtk-nor: set controller to 4B mode with large
 capacity flash

Le 31/03/2017 à 04:26, Guochun Mao a écrit :
> Hi Cyrille, Marek,
> 
> Thanks for your suggestions.
> 
> On Thu, 2017-03-30 at 19:40 +0200, Cyrille Pitchen wrote:
>> Hi Guochun,
>>
>> Le 30/03/2017 à 10:23, Guochun Mao a écrit :
>>> when nor's size larger than 16MByte, nor and controller should
>>> enter 4Byte mode simultaneously.
>>>
>>> Signed-off-by: Guochun Mao <guochun.mao@...iatek.com>
>>> ---
>>>  drivers/mtd/spi-nor/mtk-quadspi.c |    7 +++++++
>>>  1 file changed, 7 insertions(+)
>>>
>>> diff --git a/drivers/mtd/spi-nor/mtk-quadspi.c b/drivers/mtd/spi-nor/mtk-quadspi.c
>>> index e661877..05cd8a8 100644
>>> --- a/drivers/mtd/spi-nor/mtk-quadspi.c
>>> +++ b/drivers/mtd/spi-nor/mtk-quadspi.c
>>> @@ -369,6 +369,13 @@ static int mt8173_nor_write_reg(struct spi_nor *nor, u8 opcode, u8 *buf,
>>>  		/* We only handle 1 byte */
>>>  		ret = mt8173_nor_wr_sr(mt8173_nor, *buf);
>>>  		break;
>>> +	case SPINOR_OP_EN4B:
>>> +		/* Set nor controller to 4-byte address mode,
>>> +		 * and simultaneously set nor flash.
>>> +		 * This case should cooperate with default operation.
>>> +		 */
>>> +		writeb(readb(mt8173_nor->base + MTK_NOR_DUAL_REG) | 0x10,
>>> +				mt8173_nor->base + MTK_NOR_DUAL_REG);
>>
>> This is not good: you should check in both mt8173_nor_read() and
>> mt8173_nor_write() whether nor->addr_width is either 3 or 4.
>>
>> from include/linux/mtd/spi-nor.h:
>>  * @addr_width:		number of address bytes
>>
>> Besides SPI commands using an op code from 4-byte address instruction
>> set always carry a 4-byte address. They can be used directly, without
>> sending the SPINOR_OP_EN4B before. So you cannot assume that addresses
>> will be 4-byte long only if your SPI controller driver has seen a
>> SPINOR_OP_EN4B command before. This assumption is wrong.
> Nor->addr_width is assigned in spi_nor_scan in spi-nor.c, and it's not
> modified in later process.
> Does it means that we will not switch nor between 3Byte address and
> 4Byte?
> So, is it better to check nor->addr_width when do nor initialization?
>

Currently yes, nor->addr_width, nor->read_opcode, nor->read_dummy, and
nor->program_opcode are set once for all in spi_nor_scan().

However, nor->read() is likely to be called soon from spi_nor_scan()
with values of nor->addr_width, nor->read_opcode and nor->read_dummy
different from those selected when exiting spi_nor_scan().

So nor->read() / mt8173_nor_read should check nor->addr_width,
nor->read_opcode and nor->read_dummy at each call.

More precisely, I plan to use nor->read() from spi_nor_scan() to read
SFDP (Serial Flash Discoverable Parameters) data.

Whatever op code, numbers of address bytes and dummy cycles used for
(Fast) Read commands, the Read SFDP command uses fixed settings
standardized for all manufacturers and all memory parts:
- op code: 5Ah
- number of bytes for the address: 3 (even for memory > 128Mbits)
- number of dummy clock cycles: 8 clocks

https://patchwork.ozlabs.org/patch/742380/

Please have a look at the spi_nor_read_sfdp().

spi_nor_read_sfdp() is likely to be called from and only from
spi_nor_scan().

Best regards,

Cyrille

>>
>> SPI controller driver should never check SPINOR_OP_* op codes like this.
> I agree that SPI controller driver should not check SPINOR_OP_* op codes
> like what I do.
> I will correct it next version.
> 
> Best Regards,
> Guochun
>>
>> Then, testing SPINOR_OP_RDSR from mt8173_nor_read_reg() or
>> SPINOR_OP_WRSR from mt8173_nor_write_reg() is not a good practice too:
>> op codes may change depending on the memory manufacturer. So testing op
>> code values like you do can work with some memories but maybe not all.
>>
>> Finally, don't use 0x10, please define a macro instead.
>>
>> Best regards,
>>
>> Cyrille
>>
>>>  	default:
>>>  		ret = mt8173_nor_do_tx_rx(mt8173_nor, opcode, buf, len, NULL, 0);
>>>  		if (ret)
>>>
>>
> 
> 
>