Re: [PATCH] memory: renesas-rpc-if: Remove redundant division of dummy

From: Wolfram Sang <wsa+renesas@sang-engineering.com>
To: linux-renesas-soc@vger.kernel.org
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
	Mark Brown <broonie@kernel.org>,
	Sergey Shtylyov <s.shtylyov@omp.ru>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] memory: renesas-rpc-if: Remove redundant division of dummy
Date: Fri, 13 Jan 2023 09:10:12 +0100	[thread overview]
Message-ID: <Y8ER5B5D1XCTOOBX@ninjato> (raw)
In-Reply-To: <20230112090655.43367-1-wsa+renesas@sang-engineering.com>

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Using Sergei's recent email...

On Thu, Jan 12, 2023 at 10:06:55AM +0100, Wolfram Sang wrote:
> From: Cong Dang <cong.dang.xn@renesas.com>
> 
> The dummy cycles value was wrongly calculated if dummy.buswidth > 1,
> which affects QSPI, OSPI, HyperFlash on various SoCs. We're lucky in
> Single SPI case since its dummy.buswidth equals to 1, so the result of
> the division is unchanged
> 
> This issue can be reproduced using something like the following commands
> A. QSPI mode: Mount device with jffs2 format
>     jffs2: CLEANMARKER node found at 0x00000004, not first node in block (0x00000000)
> 
> B. QSPI mode: Write data to mtd10, where mtd10 is a parition on SPI Flash
> storage, defined properly in a device tree
> 
> [Correct fragment, read from SPI Flash]
> 
>   root@v3x:~# echo "hello" > /dev/mtd10
>   root@v3x:~# hexdump -C -n100 /dev/mtd10
>   00000000  68 65 6c 6c 6f 0a ff ff  ff ff ff ff ff ff ff ff  |hello...........|
>   00000010  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff  |................|
> 
> [Incorrect read of the same fragment: see the difference at offsets 0-3]
> 
>   root@v3x:~# echo "hello" > /dev/mtd10
>   root@v3x:~# hexdump -C -n100 /dev/mtd10
>   00000000  00 00 00 00 68 65 6c 6c  6f 0a ff ff ff ff ff ff  |....hello.......|
>   00000010  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff  |................|
> 
> As seen from the result, 4 NULL bytes were inserted before the test data.
> Wrong calculation in rpcif_prepare() led to miss of some dummy cycle. A
> division by bus width is redundant because it had been performed already
> in spi-rpc-if.c::rpcif_spi_mem_prepare()
> 
> Fix this by removing the redundant division.
> 
> Fixes: ca7d8b980b67 ("memory: add Renesas RPC-IF driver")
> Signed-off-by: Cong Dang <cong.dang.xn@renesas.com>
> Signed-off-by: Hai Pham <hai.pham.ud@renesas.com>
> Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
> ---
> 
> Sadly, I cannot test this patch myself because I don't have access to
> hardware which uses a buswidth > 1 for the dummy read. However, from
> code review, this patch makes sense. The division by buswidth is done
> twice, once in the SPI driver and once in the RPC core. It should stay
> only in the SPI driver.
> 
>  drivers/memory/renesas-rpc-if.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/memory/renesas-rpc-if.c b/drivers/memory/renesas-rpc-if.c
> index 09cd4318a83d..c36b407851ff 100644
> --- a/drivers/memory/renesas-rpc-if.c
> +++ b/drivers/memory/renesas-rpc-if.c
> @@ -430,8 +430,7 @@ void rpcif_prepare(struct rpcif *rpc, const struct rpcif_op *op, u64 *offs,
>  
>  	if (op->dummy.buswidth) {
>  		rpc->enable |= RPCIF_SMENR_DME;
> -		rpc->dummy = RPCIF_SMDMCR_DMCYC(op->dummy.ncycles /
> -						op->dummy.buswidth);
> +		rpc->dummy = RPCIF_SMDMCR_DMCYC(op->dummy.ncycles);
>  	}
>  
>  	if (op->option.buswidth) {
> -- 
> 2.30.2
> 

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