linux-kernel - Re: [v2] drm: mediatek: change the variable type of rdma threshold

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Message-ID: <1498098321.717.17.camel@mtksdaap41>
Date:   Thu, 22 Jun 2017 10:25:21 +0800
From:   Bibby Hsieh <bibby.hsieh@...iatek.com>
To:     Guenter Roeck <linux@...ck-us.net>
CC:     David Airlie <airlied@...ux.ie>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        <dri-devel@...ts.freedesktop.org>,
        <linux-mediatek@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        Cawa Cheng <cawa.cheng@...iatek.com>,
        "Mao Huang" <littlecvr@...omium.org>, CK Hu <ck.hu@...iatek.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        YT Shen <yt.shen@...iatek.com>,
        Yingjoe Chen <yingjoe.chen@...iatek.com>,
        "Sascha Hauer" <kernel@...gutronix.de>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [v2] drm: mediatek: change the variable type of rdma threshold

Hi, Guenter,

Thanks for your test and comment.


On Wed, 2017-06-21 at 14:14 -0700, Guenter Roeck wrote:
> On Fri, May 19, 2017 at 05:57:23PM +0800, Bibby Hsieh wrote:
> > For some greater resolution, the rdma threshold
> > variable will overflow.
> > 
> > Signed-off-by: Bibby Hsieh <bibby.hsieh@...iatek.com>
> > ---
> >  drivers/gpu/drm/mediatek/mtk_disp_rdma.c | 7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/mediatek/mtk_disp_rdma.c b/drivers/gpu/drm/mediatek/mtk_disp_rdma.c
> > index 0df05f9..9afdcd7 100644
> > --- a/drivers/gpu/drm/mediatek/mtk_disp_rdma.c
> > +++ b/drivers/gpu/drm/mediatek/mtk_disp_rdma.c
> > @@ -37,7 +37,7 @@
> >  #define DISP_REG_RDMA_FIFO_CON			0x0040
> >  #define RDMA_FIFO_UNDERFLOW_EN				BIT(31)
> >  #define RDMA_FIFO_PSEUDO_SIZE(bytes)			(((bytes) / 16) << 16)
> > -#define RDMA_OUTPUT_VALID_FIFO_THRESHOLD(bytes)		((bytes) / 16)
> > +#define RDMA_OUTPUT_VALID_FIFO_THRESHOLD(bytes) (((bytes) / 16) & 0x3ff)
> 
> I agree with the earlier comment; clamp_val() might be more appropriate here
> and would avoid unexpected results.
> 

Yep, It's a good suggestion to me, I will add clamp_val() to avoid
unexpected value, thanks.

> >  
> >  /**
> >   * struct mtk_disp_rdma - DISP_RDMA driver structure
> > @@ -109,7 +109,7 @@ static void mtk_rdma_config(struct mtk_ddp_comp *comp, unsigned int width,
> >  			    unsigned int height, unsigned int vrefresh,
> >  			    unsigned int bpc)
> >  {
> > -	unsigned int threshold;
> > +	unsigned long long threshold;
> >  	unsigned int reg;
> >  
> >  	rdma_update_bits(comp, DISP_REG_RDMA_SIZE_CON_0, 0xfff, width);
> > @@ -121,7 +121,8 @@ static void mtk_rdma_config(struct mtk_ddp_comp *comp, unsigned int width,
> >  	 * output threshold to 6 microseconds with 7/6 overhead to
> >  	 * account for blanking, and with a pixel depth of 4 bytes:
> >  	 */
> > -	threshold = width * height * vrefresh * 4 * 7 / 1000000;
> > +	threshold = (unsigned long long)width * height * vrefresh *
> > +		    4 * 7 / 1000000;
> 
> This is a 64 bit divide operation. It will result in a build failure
> if compiled for a 32 bit kernel (eg arm:allmodconfig).
> 
> ERROR: "__aeabi_uldivmod" [drivers/gpu/drm/mediatek/mediatek-drm.ko] undefined!
> 

Sorry about the lack of tests, I will change the divide operation to
div_u64 function, thanks for your suggestions.


> Guenter

-- 
Bibby