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

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Date:   Fri, 11 Nov 2022 04:16:03 +0000
From:   Bayi Cheng (程八意) 
        <bayi.cheng@...iatek.com>
To:     "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>,
        "David.Laight@...LAB.COM" <David.Laight@...LAB.COM>,
        "broonie@...nel.org" <broonie@...nel.org>
CC:     "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "gch981213@...il.com" <gch981213@...il.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

On Fri, 2022-11-04 at 07:53 +0000, Bayi Cheng (程八意) wrote:
> On Thu, 2022-11-03 at 22:35 +0000, David Laight wrote:
> > 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
> > 
> 
> Hi David & Angelo
> 
> Thank you for your comments!
> To sum up, I think the next version will make the following two
> changes:
> 1, The timeout value will not exceed u32, so the type of timeout will
> be changed from ulong to u32.
> 2, Change msecs_to_jiffies(max_t(size_t, timeout / 1000, 10)) to be
> msecs_to_jiffies(max(timeout / 1000, 10U)).
> 
> If you think these changes are not enough, please let me know,
> Thanks！
> 
> Best Regards,
> Bayi
> 

Hi Angelo, Hi David,

Just a gentle ping on this.
Could you please review this patch and give us some suggestion?

PS: With your permission, I will make the following changes in the next
version:

Change in v2:
  -Change the type of "timeout" from ulong to u32.
  -Replace max_t with max.


Thanks.

BRs,
Bayi Cheng

> > > 
> > > 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
> > 
> > -
> > Registered Address Lakeside, Bramley Road, Mount Farm, Milton
> > Keynes,
> > MK1 1PT, UK
> > Registration No: 1397386 (Wales)