linux-kernel - RE: [PATCH v1] spi: spi-mtk-nor: Optimize timeout for dma read

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Date:   Thu, 3 Nov 2022 22:35:09 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'AngeloGioacchino Del Regno' 
        <angelogioacchino.delregno@...labora.com>,
        Bayi Cheng <bayi.cheng@...iatek.com>,
        Mark Brown <broonie@...nel.org>
CC:     Matthias Brugger <matthias.bgg@...il.com>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        Chuanhong Guo <gch981213@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "srv_heupstream@...iatek.com" <srv_heupstream@...iatek.com>,
        Project_Global_Chrome_Upstream_Group 
        <Project_Global_Chrome_Upstream_Group@...iatek.com>
Subject: RE: [PATCH v1] spi: spi-mtk-nor: Optimize timeout for dma read

From: AngeloGioacchino Del Regno
> Sent: 03 November 2022 09:44
> 
> Il 03/11/22 06:28, Bayi Cheng ha scritto:
> > From: bayi cheng <bayi.cheng@...iatek.com>
> >
> > The timeout value of the current dma read is unreasonable. For example,
> > If the spi flash clock is 26Mhz, It will takes about 1.3ms to read a
> > 4KB data in spi mode. But the actual measurement exceeds 50s when a
> > dma read timeout is encountered.
> >
> > In order to be more accurately, It is necessary to use msecs_to_jiffies,
> > After modification, the measured timeout value is about 130ms.
> >
> > Signed-off-by: bayi cheng <bayi.cheng@...iatek.com>
> > ---
> >   drivers/spi/spi-mtk-nor.c | 7 ++++---
> >   1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/spi/spi-mtk-nor.c b/drivers/spi/spi-mtk-nor.c
> > index d167699a1a96..3d989db80ee9 100644
> > --- a/drivers/spi/spi-mtk-nor.c
> > +++ b/drivers/spi/spi-mtk-nor.c
> > @@ -354,7 +354,7 @@ static int mtk_nor_dma_exec(struct mtk_nor *sp, u32 from, unsigned int length,
> >   			    dma_addr_t dma_addr)
> >   {
> >   	int ret = 0;
> > -	ulong delay;
> > +	ulong delay, timeout;
> >   	u32 reg;
> >
> >   	writel(from, sp->base + MTK_NOR_REG_DMA_FADR);
> > @@ -376,15 +376,16 @@ static int mtk_nor_dma_exec(struct mtk_nor *sp, u32 from, unsigned int length,
> >   	mtk_nor_rmw(sp, MTK_NOR_REG_DMA_CTL, MTK_NOR_DMA_START, 0);
> >
> >   	delay = CLK_TO_US(sp, (length + 5) * BITS_PER_BYTE);
> > +	timeout = (delay + 1) * 100;
> >
> >   	if (sp->has_irq) {
> >   		if (!wait_for_completion_timeout(&sp->op_done,
> > -						 (delay + 1) * 100))
> > +		    msecs_to_jiffies(max_t(size_t, timeout / 1000, 10))))
> 
> You're giving a `size_t` variable to msecs_to_jiffies(), but checking `jiffies.h`,
> this function takes a `const unsigned int` param.
> Please change the type to match that.

The type shouldn't matter at all.
What matters is the domain of the value.

Quite why you need to use max_t(size_t, ...) is another matter.
timeout is ulong so max(timeout/1000, 10ul) should be fine.

But is ulong even right?
The domain of the value is almost certainly the same on 32bit and 64bit.
So you almost certainly need u32 or u64.

	David

> 
> Aside from that, your `timeout` variable contains a timeout in microseconds and
> this means that actually using msecs_to_jiffies() is suboptimal here.
> 
> Please use usecs_to_jiffies() instead.
> 
> Regards,
> Angelo

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