linux-kernel - Re: [mtd:nand/next 11/31] drivers/mtd/nand/raw/cadence-nand-controller.c:1893:4: error: implicit declaration of function 'ioread64

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Message-Id: <e0a3bc54-a1be-4e10-afcb-bee1888c4066@www.fastmail.com>
Date:   Tue, 27 Sep 2022 22:02:39 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Valentin Korenblit" <vkorenblit@...uans.com>,
        "Miquel Raynal" <miquel.raynal@...tlin.com>
Cc:     "kernel test robot" <lkp@...el.com>, llvm@...ts.linux.dev,
        kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org
Subject: Re: [mtd:nand/next 11/31]
 drivers/mtd/nand/raw/cadence-nand-controller.c:1893:4: error: implicit
 declaration of function 'ioread64_rep' is invalid in C99

On Tue, Sep 27, 2022, at 4:56 PM, Valentin Korenblit wrote:
>>> 
>>> But in the mean time I am only half satisfied, because we plan to do
>>> twice more accesses than needed _just_ because of a the COMPILE_TEST
>>> constraint.
>> In my example, I had an #ifdef so it would only fall back
>> to 32-bit accesses on the 64-bit register when running an
>> actual 32-bit kernel, but leaving the 64-bit case efficient. Sorry for my late reply. I've just tested this and unfortunately
> the two sequential 32-bit accesses (with OFF0==0 and OFF1==4 seem
> to trigger sdma_err. I need to check some waveforms to verify if it 
> happens right after the first access. 

What happens if you do pairs of read from offset 0, effectively
doing a readsl() instead of readql(), obviously with twice the number
of accesses.

It's also possible you have to read from the second word first,
like

  u32 *buf;
  do {
     buf[1] = __raw_readl(reg + 4);
     buf[0] = __raw_readl(reg);
     buf += 2;
  }  while (buf < end);

   Arnd