linux-kernel - Re: [PATCH RFC] spi-nor: provide a range for poll

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Date:   Sun, 12 Feb 2017 22:59:23 +0100
From:   Boris Brezillon <boris.brezillon@...e-electrons.com>
To:     Nicholas Mc Guire <der.herr@...r.at>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:     Cyrille Pitchen <cyrille.pitchen@...el.com>,
        Marek Vasut <marek.vasut@...il.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Richard Weinberger <richard@....at>,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] spi-nor: provide a range for poll_timout

+Mika

On Sun, 12 Feb 2017 17:42:57 +0100
Nicholas Mc Guire <der.herr@...r.at> wrote:

> The overall poll time here is INTEL_SPI_TIMEOUT * 1000 which is 
> 5000 * 1000 - so 5seconds and it is coded as a tight loop here delay_us
> to readl_poll_timeout() is set to 0. As this is never called in an atomic
> context sleeping should be no issue and there is no reasons for the
> tight-loop here.

Hm, let's wait for Mika's feedback on this one. BTW, can you please Cc
him on you other spi-nor/intel patches and prefix your patches with the
driver name ('mtd: spi-nor: intel: ') so that we know where the changes
are made (without this prefix it looks like you're touching core files)?

Thanks,

Boris

> 
> Signed-off-by: Nicholas Mc Guire <der.herr@...r.at>
> ---
> 
> Problem located by experimental coccinelle script:
> ./drivers/mtd/spi-nor/intel-spi.c:265:8-26: WARNING: usleep_range min=0 for delay INTEL_SPI_TIMEOUT * 1000
> ./drivers/mtd/spi-nor/intel-spi.c:274:8-26: WARNING: usleep_range min=0 for delay INTEL_SPI_TIMEOUT * 1000
> 
> The rational for setting the delay_us here to 40 is that readx_poll_timeout()
> will take delay_us >> 2 + 1 as min value and that should be at least 10us (see
> Documentation/timers/timers-howto.txt). Ideally the delay would be made
> even larger to keep the load on the hrtimer subsystem low as these delays
> here do not seem to be critical. Someone that knows the details of this device
> would need to check if a larger delay would be ok here.
> 
> Patch was compile tested with: multi_v7_defconfig (implies CONFIG_MTD_SPI_NOR=y)
> one coccicheck finding reported and one spars finding (in separate patches)
> 
> Patch is against 4.10-rc6 (localversion-next is next-20170210)
> 
>  drivers/mtd/spi-nor/intel-spi.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mtd/spi-nor/intel-spi.c b/drivers/mtd/spi-nor/intel-spi.c
> index a10f602..371bcf9 100644
> --- a/drivers/mtd/spi-nor/intel-spi.c
> +++ b/drivers/mtd/spi-nor/intel-spi.c
> @@ -263,7 +263,7 @@ static int intel_spi_wait_hw_busy(struct intel_spi *ispi)
>  	u32 val;
>  
>  	return readl_poll_timeout(ispi->base + HSFSTS_CTL, val,
> -				  !(val & HSFSTS_CTL_SCIP), 0,
> +				  !(val & HSFSTS_CTL_SCIP), 40,
>  				  INTEL_SPI_TIMEOUT * 1000);
>  }
>  
> @@ -272,7 +272,7 @@ static int intel_spi_wait_sw_busy(struct intel_spi *ispi)
>  	u32 val;
>  
>  	return readl_poll_timeout(ispi->sregs + SSFSTS_CTL, val,
> -				  !(val & SSFSTS_CTL_SCIP), 0,
> +				  !(val & SSFSTS_CTL_SCIP), 40,
>  				  INTEL_SPI_TIMEOUT * 1000);
>  }
>