Re: [PATCH 1/2] spi/rockchip: fix bug that case spi can't go as fast as slave request

From: Mark Brown <broonie@kernel.org>
To: addy ke <addy.ke@rock-chips.com>
Cc: heiko@sntech.de, kever.yang@rock-chips.com,
	linux-kernel@vger.kernel.org, xjq@rock-chips.com,
	zyw@rock-chips.com, linux-rockchip@lists.infradead.org,
	grant.likely@linaro.org, hj@rock-chips.com,
	huangtao@rock-chips.com, devicetree@vger.kernel.org,
	amstan@google.com, yzq@rock-chips.com, zhangqing@rock-chips.com,
	cf@rock-chips.com, robh+dt@kernel.org,
	linux-arm-kernel@lists.infradead.org, hl@rock-chips.com,
	dianders@chromium.org, linux-spi@vger.kernel.org,
	wei.luo@rock-chips.com, sonnyrao@google.com, olof@lixom.net,
	zhenfu.fang@rock-chips.com
Subject: Re: [PATCH 1/2] spi/rockchip: fix bug that case spi can't go as fast as slave request
Date: Thu, 16 Oct 2014 11:34:10 +0200	[thread overview]
Message-ID: <20141016093410.GB2200@sirena.org.uk> (raw)
In-Reply-To: <543F8CD2.1010302@rock-chips.com>

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On Thu, Oct 16, 2014 at 05:16:02PM +0800, addy ke wrote:
> On 2014/10/15 21:04, Mark Brown wrote:
> > On Wed, Oct 15, 2014 at 07:25:49PM +0800, Addy Ke wrote:

> >> +	if (WARN_ON(rs->speed > MAX_SCLK_OUT))
> >> +		rs->speed = MAX_SCLK_OUT;

> >> +	/* the minimum divsor is 2 */
> >> +	if (rs->max_freq < 2 * rs->speed) {
> >> +		clk_set_rate(rs->spiclk, 2 * rs->speed);
> >> +		rs->max_freq = clk_get_rate(rs->spiclk);
> >> +	}

> > I'll apply this but you should be checking the return code from
> > clk_set_rate() here, please send a followup patch doing that.  It might

> If clk_set_rate return error, do I only put dev_warn here or return error value to spi core?

It'd be better to return an error if we need to set the rate and can't
do it.

> > also be worth consdering just setting the rate unconditionally here, it
> > seems like it should make things simpler.

> I think we need.
> If we set the rate unconditionally here, clk_set_rate() will be executed in each spi transfer.

Is that really such a high cost?

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