linux-kernel - Re: [PATCH v10 1/5] mtd: nand: vf610_nfc: Freescale NFC for VF610, MPC5125 and others

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Message-ID: <20150825201631.GK81844@google.com>
Date:	Tue, 25 Aug 2015 13:16:31 -0700
From:	Brian Norris <computersforpeace@...il.com>
To:	Stefan Agner <stefan@...er.ch>
Cc:	dwmw2@...radead.org, sebastian@...akpoint.cc, robh+dt@...nel.org,
	pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	shawn.guo@...aro.org, kernel@...gutronix.de,
	boris.brezillon@...e-electrons.com, marb@...at.de,
	aaron@...tycactus.com, bpringlemeir@...il.com,
	linux-mtd@...ts.infradead.org, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	albert.aribaud@...ev.fr, klimov.linux@...il.com,
	Bill Pringlemeir <bpringlemeir@...ps.com>
Subject: Re: [PATCH v10 1/5] mtd: nand: vf610_nfc: Freescale NFC for VF610,
 MPC5125 and others

A few more comments.

On Mon, Aug 03, 2015 at 11:27:26AM +0200, 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..5c8dfe8
> --- /dev/null
> +++ b/drivers/mtd/nand/vf610_nfc.c
> @@ -0,0 +1,645 @@

...

> +/*
> + * This function supports Vybrid only (MPC5125 would have full RB and four CS)
> + */
> +static void vf610_nfc_select_chip(struct mtd_info *mtd, int chip)
> +{
> +#ifdef CONFIG_SOC_VF610

Why the #ifdef? I don't see anything compile-time specific to SOC_VF610.

If this is trying to handle the comment above ("This function supports
Vybrid only (MPC5125 would have full RB and four CS)") then that's the
wrong way of doing it, as you need to support multiplatform kernels.
You'll need to have a way to differentiate the different platform
support at runtime, not compile time.

> +	struct vf610_nfc *nfc = mtd_to_nfc(mtd);
> +	u32 tmp = vf610_nfc_read(nfc, NFC_ROW_ADDR);
> +
> +	tmp &= ~(ROW_ADDR_CHIP_SEL_RB_MASK | ROW_ADDR_CHIP_SEL_MASK);
> +	tmp |= 1 << ROW_ADDR_CHIP_SEL_RB_SHIFT;
> +
> +	if (chip == 0)
> +		tmp |= 1 << ROW_ADDR_CHIP_SEL_SHIFT;
> +	else if (chip == 1)
> +		tmp |= 2 << ROW_ADDR_CHIP_SEL_SHIFT;

	else ... ?

Maybe you can write this as a formulaic pattern (e.g.:

	tmp |= (chip + 1) << ROW_ADDR_CHIP_SEL_SHIFT;

) and just do the "max # of chips" checks on a per-platform basis in the
probe(). Then I'm guessing this same function can apply to both
platforms. (I'm not looking at HW datasheets for this, BTW, just
guessing based on the context here.)

But wait...I see that you call nand_scan_ident() with a max of 1 chip.
So you won't ever see the chip > 0 case, right?

So does this driver support multiple flash attached or not? Looks like
you're assuming you'll only be using chip-select 0. (This is fine for
now, but at least your code should acknowledge this. Perhaps a comment
at the top under "limitations.")

> +
> +	vf610_nfc_write(nfc, NFC_ROW_ADDR, tmp);
> +#endif
> +}

...

> +static int vf610_nfc_probe(struct platform_device *pdev)
> +{

...

> +	/* first scan to find the device and get the page size */
> +	if (nand_scan_ident(mtd, 1, NULL)) {
> +		err = -ENXIO;
> +		goto error;
> +	}

...

Brian
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