Re: [RFC 07/47] mtd: nand: stm_nand_bch: initialise the BCH Controller

Lee Jones
2014-04-30T12:30:17Z

> >> >+ /* Reset and disable boot-mode controller */
> >> >+ writel(BOOT_CFG_RESET, nandi->base + NANDBCH_BOOTBANK_CFG);
> >> >+ udelay(1);
> >> >+ writel(0x00000000, nandi->base + NANDBCH_BOOTBANK_CFG);
> >>
> >> Why using 'udelay' ?
> >> Isn't there any status register which tells you that controller is reset / initialized ?
> >> Or may be polling on NANDBCH_BOOTBANK_CFG may itself give you status.
> >
> >Documenation says:
> >
> > "The soft reset bit has to be reset to ‘0’ to de-assert the soft
> > reset. The soft reset bit is expected to be asserted for at least
> > one clock cycle for proper reset"
> >
> That’s the hardware way of saying that 'enable the clock before applying reset'.
> Clock is required to propagate reset-logic to flip-flops in pipeline, which do not get direct reset.
>
> However that apart. You may safely drop udelay(1) because this 'udelay' is at
> CPU side and won't guarantee anything about clocks at your controller side.
> But I leave it to you as this delay is pretty small.

I'd like to keep it in if it's all the same to you. The original
author is pretty competent and I like to think that it's there for a
reason - and as you rightly say, the delay is pretty small.

--
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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