linux-kernel - Re: [PATCH 4.4 017/192] [PATCH 017/135] clk: xgene: Fix divider with non-zero shift value

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Message-ID: <1474371589.31504.4.camel@codethink.co.uk>
Date:   Tue, 20 Sep 2016 12:39:49 +0100
From:   Ben Hutchings <ben.hutchings@...ethink.co.uk>
To:     Loc Ho <lho@....com>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Stephen Boyd <sboyd@...eaurora.org>,
        Sasha Levin <alexander.levin@...izon.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 4.4 017/192] [PATCH 017/135] clk: xgene: Fix divider
 with non-zero shift value

On Mon, 2016-09-12 at 18:58 +0200, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> [ Upstream commit 1382ea631ddddb634850a3795527db0feeff5aaf ]
> 
> The X-Gene clock driver missed the divider shift operation when
> set the divider value.
> 
> Signed-off-by: Loc Ho <lho@....com>
> Fixes: 308964caeebc ("clk: Add APM X-Gene SoC clock driver")
> Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
> Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
>  drivers/clk/clk-xgene.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> --- a/drivers/clk/clk-xgene.c
> +++ b/drivers/clk/clk-xgene.c
> @@ -351,7 +351,8 @@ static int xgene_clk_set_rate(struct clk
>  		/* Set new divider */
>  		data = xgene_clk_read(pclk->param.divider_reg +
>  				pclk->param.reg_divider_offset);
> -		data &= ~((1 << pclk->param.reg_divider_width) - 1);
> +		data &= ~((1 << pclk->param.reg_divider_width) - 1)
> +				<< pclk->param.reg_divider_shift;
[...]

This still does the wrong thing when the shift value is non-zero: it
clears all bits to the right of the divider field in data.  I think the
correct assignment is:

		data &= ~(((1 << pclk->param.reg_divider_width) - 1)
		          << pclk->param.reg_divider_shift);

Ben.

-- 
Ben Hutchings
Software Developer, Codethink Ltd.