Re: Questions about the Freescale/NXP QuadSPI controller

[Boris Brezillon <boris.brezillon@bootlin.com>]

Hi Han,

On Thu, 2 Aug 2018 21:58:48 +0000
Han Xu <han.xu@nxp.com> wrote:

> > -----Original Message-----
> > From: Frieder Schrempf [mailto:frieder.schrempf@exceet.de]
> > Sent: Thursday, August 2, 2018 8:09 AM
> > To: David Wolfe <david.wolfe@nxp.com>; Fabio Estevam
> > <fabio.estevam@nxp.com>; Prabhakar Kushwaha
> > <prabhakar.kushwaha@nxp.com>; Yogesh Narayan Gaur
> > <yogeshnarayan.gaur@nxp.com>; Han Xu <han.xu@nxp.com>;
> > shawnguo@kernel.org
> > Cc: linux-mtd@lists.infradead.org; boris.brezillon@bootlin.com; linux-
> > spi@vger.kernel.org; dwmw2@infradead.org;
> > computersforpeace@gmail.com; marek.vasut@gmail.com; richard@nod.at;
> > miquel.raynal@bootlin.com; broonie@kernel.org
> > Subject: Re: Questions about the Freescale/NXP QuadSPI controller
> > 
> > Ping.
> > 
> > I'm not sure if my message below went out to you at all. At least I can't find it
> > in the ML archive.
> > 
> > I still hope someone can help with the questions below.
> > 
> > Meanwhile for the second point I did some tests myself with one chip on
> > each of the two buses and it worked fine with my latest v2 patches.
> > So I'm not sure at all why Yogesh has problems with his setup (two chips on
> > the first bus).  
> 
> Tried to test the v2 patch set on i.MX6SX SDB board but get the memory map failure.
> 
> [    1.298633] fsl-quadspi 21e4000.qspi: ioremap failed for resource [mem 0x70000000-0x7fffffff]
> [    1.307330] fsl-quadspi 21e4000.qspi: Freescale QuadSPI probe failed
> [    1.313922] fsl-quadspi: probe of 21e4000.qspi failed with error -12
> 
> This is the reason why dynamic ioremap added in previous driver, please refer to
>  https://patchwork.ozlabs.org/patch/503655/

We can reduce the size of the iomap to 2k * 4, since this is all we use
currently. Can you try to change the size of the ioremap call to 16k and
tell us if it works.

Unrelated to this issue, we still have 2 questions left unanswered:

1/ is there an easy way to invalidate AHB buffers? I mean, not
   something that implies a full reset + several milliseconds of delay
   after the reset. Right now we trick the caching logic by mapping a
   portion that is twice the size of the buffer and switching from one
   sub-portion to this other to trigger a real read on each read
   access, but that's hack-ish, and I'd be surprised if HW
   engineers hadn't planned for this "manual AHB buffer flush" case.

2/ if we use DMA, do you know what happens when the TX FIFO runs out
   of data while the TX request is not finished yet. In PIO mode, it
   seems the engine sends garbage on the bus when that happens, and we
   definitely don't want that.

While #1 is not blocking us, #2 is if we don't have those patches
[1][2] applied, and Marek wanted to be sure there was no other
ways to solve the "TX FIFO starvation" issue before considering these
changes. So that'd be great if someone from NXP could have a look/ask
around and give us answers to those 2 questions.

Thanks,

Boris

[1]http://patchwork.ozlabs.org/patch/928677/
[2]http://patchwork.ozlabs.org/patch/928678/

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