linux-kernel - Re: [PATCH v4 1/6] mtd: nand: vf610_nfc: Freescale NFC for VF610, MPC5125 and others

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Date:	Wed, 03 Jun 2015 17:05:16 +0200
From:	Stefan Agner <stefan@...er.ch>
To:	Sebastian Andrzej Siewior <sebastian@...akpoint.cc>
Cc:	dwmw2@...radead.org, computersforpeace@...il.com,
	mark.rutland@....com, boris.brezillon@...e-electrons.com,
	aaron@...tycactus.com, marb@...at.de, pawel.moll@....com,
	ijc+devicetree@...lion.org.uk, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, robh+dt@...nel.org,
	linux-mtd@...ts.infradead.org, kernel@...gutronix.de,
	galak@...eaurora.org, shawn.guo@...aro.org,
	linux-arm-kernel@...ts.infradead.org, bpringlemeir@...ps.com
Subject: Re: [PATCH v4 1/6] mtd: nand: vf610_nfc: Freescale NFC for VF610, MPC5125 and others

On 2015-06-03 15:08, Sebastian Andrzej Siewior wrote:
> On 2015-03-25 17:28:24 [+0100], Stefan Agner wrote:
>> diff --git a/drivers/mtd/nand/vf610_nfc.c b/drivers/mtd/nand/vf610_nfc.c
>> new file mode 100644
>> index 0000000..23c1510
>> --- /dev/null
>> +++ b/drivers/mtd/nand/vf610_nfc.c
>> @@ -0,0 +1,686 @@
> …
>> +static inline u32 vf610_nfc_read(struct vf610_nfc *nfc, uint reg)
>> +{
>> +	return readl(nfc->regs + reg);
>> +}
>> +
>> +static inline void vf610_nfc_write(struct vf610_nfc *nfc, uint reg, u32 val)
>> +{
>> +	writel(val, nfc->regs + reg);
>> +}
> …
> 
>> +static void vf610_nfc_send_command(struct vf610_nfc *nfc, u32 cmd_byte1,
>> +				   u32 cmd_code)
>> +{
>> +	void __iomem *reg = nfc->regs + NFC_FLASH_CMD2;
>> +	u32 tmp;
>> +
>> +	vf610_nfc_clear_status(nfc);
>> +
>> +	tmp = __raw_readl(reg);
>> +	tmp &= ~(CMD_BYTE1_MASK | CMD_CODE_MASK | BUFNO_MASK);
>> +	tmp |= cmd_byte1 << CMD_BYTE1_SHIFT;
>> +	tmp |= cmd_code << CMD_CODE_SHIFT;
>> +	__raw_writel(tmp, reg);
>> +}
> 
> Why readl() vs __raw_readl() dito for write?
> vf610_nfc_{read|write} is good since for PPC we would need out_be32()
> here instead.
> It would be nice if you could abstract the __raw_ once as well. And I am
> not sure if you need those at all since the former functions should work
> here just fine.

As Boris guessed correctly, the reason I used the raw variant was due to
performance improvements due to the barrier. However, I will use
{read|write}l_relaxed instead, which should offer endian abstraction
while not having the performance penalty due to extensive barriers...

--
Stefan

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