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

[Bayi Cheng (程八意)]

On Fri, 2022-11-11 at 10:16 +0100, AngeloGioacchino Del Regno wrote:
> Il 11/11/22 05:16, Bayi Cheng (程八意) ha scritto:
> > 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 at mediatek.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 at mediatek.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.
> > 
> 
> I still recommend to use usecs_to_jiffies() when appropriate, instead
> of
> converting usecs to msecs and using msecs_to_jiffies().
> 
> As for the rest in your list: yes, please.
> 
> Regards,
> Angelo
> 

Hi Angelo,

Thanks for your comments! 
I will change it to be usecs_to_jiffies(max(timeout, 10000U)) in the
next patch.

BRs,
Bayi Cheng


> > 
> > 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)
> 
>