linux-kernel - Re: [PATCH v3 03/13] spi: atmel-quadspi: drop wrappers for iomem accesses

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Date:   Sat, 2 Feb 2019 14:23:37 +0100
From:   Boris Brezillon <bbrezillon@...nel.org>
To:     <Tudor.Ambarus@...rochip.com>
Cc:     <mark.rutland@....com>, <devicetree@...r.kernel.org>,
        <alexandre.belloni@...tlin.com>, <linux-kernel@...r.kernel.org>,
        <Cyrille.Pitchen@...rochip.com>, <Nicolas.Ferre@...rochip.com>,
        <robh+dt@...nel.org>, <linux-spi@...r.kernel.org>,
        <Ludovic.Desroches@...rochip.com>, <broonie@...nel.org>,
        <linux-mtd@...ts.infradead.org>, <bugalski.piotr@...il.com>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 03/13] spi: atmel-quadspi: drop wrappers for iomem
 accesses

On Sat, 2 Feb 2019 08:44:27 +0000
<Tudor.Ambarus@...rochip.com> wrote:

> On 02/02/2019 09:11 AM, Boris Brezillon wrote:
> > On Sat, 2 Feb 2019 04:07:19 +0000
> > <Tudor.Ambarus@...rochip.com> wrote:
> >   
> >> From: Tudor Ambarus <tudor.ambarus@...rochip.com>
> >>
> >> The wrappers hid that the accesses are relaxed. Drop them.
> >>
> >> Suggested-by: Boris Brezillon <bbrezillon@...nel.org>
> >> Signed-off-by: Tudor Ambarus <tudor.ambarus@...rochip.com>
> >> ---
> >> v3: no change
> >> v2: new patch
> >>
> >>  drivers/spi/atmel-quadspi.c | 47 +++++++++++++++++++--------------------------
> >>  1 file changed, 20 insertions(+), 27 deletions(-)
> >>
> >> diff --git a/drivers/spi/atmel-quadspi.c b/drivers/spi/atmel-quadspi.c
> >> index feeddcb25e1f..131374db0db4 100644
> >> --- a/drivers/spi/atmel-quadspi.c
> >> +++ b/drivers/spi/atmel-quadspi.c
> >> @@ -175,17 +175,6 @@ static const struct qspi_mode sama5d2_qspi_modes[] = {
> >>  	{ 4, 4, 4, QSPI_IFR_WIDTH_QUAD_CMD },
> >>  };
> >>  
> >> -/* Register access functions */
> >> -static inline u32 qspi_readl(struct atmel_qspi *aq, u32 reg)
> >> -{
> >> -	return readl_relaxed(aq->regs + reg);
> >> -}
> >> -
> >> -static inline void qspi_writel(struct atmel_qspi *aq, u32 reg, u32 value)
> >> -{
> >> -	writel_relaxed(value, aq->regs + reg);
> >> -}
> >> -
> >>  static inline bool is_compatible(const struct spi_mem_op *op,
> >>  				 const struct qspi_mode *mode)
> >>  {
> >> @@ -229,6 +218,7 @@ static bool atmel_qspi_supports_op(struct spi_mem *mem,
> >>  static int atmel_qspi_exec_op(struct spi_mem *mem, const struct spi_mem_op *op)
> >>  {
> >>  	struct atmel_qspi *aq = spi_controller_get_devdata(mem->spi->master);
> >> +	void __iomem *base = aq->regs;  
> > 
> > Can we name this variable regs instead of base or even get rid of it
> > and dereference aq->regs in the xxx_relaxed() calls (doesn't look like
> > the lines would be over 80 chars even when doing that). With this
> > addressed, you can add:
> > 
> > Reviewed-by: Boris Brezillon <bbrezillon@...nel.org>  
> 
> I chose to introduce the "base" variable when I have at least 2 dereferences in
> a function, as an optimization. In exec_op() for example, there are 6
> dereferences of aq->reqs. Why do you prefer keeping aq->regs?

I tend to not add local variables unless they help improve readability
or optimize things. In this case, I'd expect the compiler to be smart
enough to detect that aq->reqs is used several times and store it in a
register. When it comes to readability, I don't think it improve
things, but that's probably a matter of taste.