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

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Message-ID: <10529948-a9b8-2121-7adb-0e94cf3cbf6a@collabora.com>
Date:   Thu, 3 Nov 2022 10:43:41 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Bayi Cheng <bayi.cheng@...iatek.com>,
        Mark Brown <broonie@...nel.org>
Cc:     Matthias Brugger <matthias.bgg@...il.com>,
        linux-spi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Chuanhong Guo <gch981213@...il.com>,
        linux-kernel@...r.kernel.org, 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

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.

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