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From: Grant Likely <grant.likely-s3s/WqlpOiPyB63q8FvJNQ@public.gmane.org>
To: thomas.koeller-x9WYMywdo8BF6kxbq+BtvQ@public.gmane.org
Cc: Sudhakar Rajashekhara <sudhakar.raj-l0cyMroinI0@public.gmane.org>,
	Kevin Hilman
	<khilman-1D3HCaltpLuhEniVeURVKkEOCMrvLtNR@public.gmane.org>,
	Sandeep Paulraj <s-paulraj-l0cyMroinI0@public.gmane.org>,
	Philby John <pjohn-k0rHJ+Hhz/SB+jHODAdFcQ@public.gmane.org>,
	spi-devel-general-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org,
	davinci-linux-open-source-VycZQUHpC/Nq7ICLvS4PUAC/G2K4zDHf@public.gmane.org
Subject: Re: [PATCH] DaVinci SPI: Fix SPI clock prescale factor computation
Date: Mon, 26 Apr 2010 09:06:11 -0600	[thread overview]
Message-ID: <k2zfa686aa41004260806r691e1880i2a80b102c108be5a@mail.gmail.com> (raw)
In-Reply-To: <1272272505-5021-2-git-send-email-thomas.koeller-x9WYMywdo8BF6kxbq+BtvQ@public.gmane.org>

On Mon, Apr 26, 2010 at 3:01 AM,  <thomas.koeller-x9WYMywdo8BF6kxbq+BtvQ@public.gmane.org> wrote:
> From: Thomas Koeller <thomas.koeller-x9WYMywdo8BF6kxbq+BtvQ@public.gmane.org>
>
> Computation of the clock prescaler value returned bogus results if
> the requested SPI clock was impossible to set. It now sets either
> the maximum or minimum clock frequency, as appropriate.
>
> Signed-off-by: Thomas Koeller <thomas.koeller-x9WYMywdo8BF6kxbq+BtvQ@public.gmane.org>
> ---
>  drivers/spi/davinci_spi.c |   12 +++++++++---
>  1 files changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/spi/davinci_spi.c b/drivers/spi/davinci_spi.c
> index 956f617..02e1a76 100644
> --- a/drivers/spi/davinci_spi.c
> +++ b/drivers/spi/davinci_spi.c
> @@ -153,7 +153,7 @@ static int davinci_spi_setup_transfer(struct spi_device *spi,
>        struct davinci_spi *davinci_spi;
>        struct davinci_spi_platform_data *pdata;
>        u8 bits_per_word = 0;
> -       u32 hz = 0, prescale;
> +       u32 hz = 0, prescale = 0, clkspeed;
>
>        davinci_spi = spi_master_get_devdata(spi->master);
>        pdata = davinci_spi->pdata;
> @@ -190,10 +190,16 @@ static int davinci_spi_setup_transfer(struct spi_device *spi,
>        set_fmt_bits(davinci_spi->base, bits_per_word & 0x1f,
>                        spi->chip_select);
>
> -       prescale = ((clk_get_rate(davinci_spi->clk) / hz) - 1) & 0xff;
> +       clkspeed = clk_get_rate(davinci_spi->clk);
> +       if (hz > clkspeed / 2)
> +               prescale = 1 << 8;
> +       if (hz < clkspeed / 256)
> +               prescale = 255 << 8;
> +       if (!prescale)
> +               prescale = ((clkspeed / hz - 1) << 8) & 0x0000ff00;

Is be appropriate to WARN_ON() or WARN_ONCE() when the clamp condition
occurs?  Particularly the condition where the minimum clock speed is
higher that the requested clock.

I'd also consider an if / else if / else structure for readability and clarity.

g.

------------------------------------------------------------------------------

  parent reply	other threads:[~2010-04-26 15:06 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <871veaksca.fsf@deeprootsystems.com>
     [not found] ` <871veaksca.fsf-1D3HCaltpLuhEniVeURVKkEOCMrvLtNR@public.gmane.org>
2010-04-26  9:01   ` [PATCH] DaVinci SPI: Fix SPI clock prescale factor computation thomas.koeller-x9WYMywdo8BF6kxbq+BtvQ
2010-04-26  9:01   ` thomas.koeller-x9WYMywdo8BF6kxbq+BtvQ
     [not found]     ` <1272272505-5021-2-git-send-email-thomas.koeller-x9WYMywdo8BF6kxbq+BtvQ@public.gmane.org>
2010-04-26 15:06       ` Grant Likely [this message]
     [not found]         ` <k2zfa686aa41004260806r691e1880i2a80b102c108be5a-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2010-05-31 14:33           ` thomas.koeller-x9WYMywdo8BF6kxbq+BtvQ

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