linux-kernel - Re: [PATCH] mtd: nand: raw: qcom_nandc: Don't clear_bam

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Date:   Fri, 14 Jan 2022 08:27:18 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Konrad Dybcio <konrad.dybcio@...ainline.org>
Cc:     ~postmarketos/upstreaming@...ts.sr.ht, martin.botka@...ainline.org,
        angelogioacchino.delregno@...ainline.org,
        marijn.suijten@...ainline.org, jamipkettunen@...ainline.org,
        Manivannan Sadhasivam <mani@...nel.org>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        linux-mtd@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, mdalam@...eaurora.org,
        sricharan@...eaurora.org
Subject: Re: [PATCH] mtd: nand: raw: qcom_nandc: Don't clear_bam_transaction
 on READID

Hi Konrad,

konrad.dybcio@...ainline.org wrote on Thu, 13 Jan 2022 19:44:26 +0100:

> While I have absolutely 0 idea why and how, running clear_bam_transaction
> when READID is issued makes the DMA totally clog up and refuse to function
> at all on mdm9607. In fact, it is so bad that all the data gets garbled
> and after a short while in the nand probe flow, the CPU decides that
> sepuku is the only option.
> 
> Removing _READID from the if condition makes it work like a charm, I can
> read data and mount partitions without a problem.
> 
> Signed-off-by: Konrad Dybcio <konrad.dybcio@...ainline.org>
> ---
> This is totally just an observation which took me an inhumane amount of
> debug prints to find.. perhaps there's a better reason behind this, but
> I can't seem to find any answers.. Therefore, this is a BIG RFC!

I'm adding two people from codeaurora who worked a lot on this driver.
Hopefully they will have an idea :)

Thanks,Miquèl

> 
> 
>  drivers/mtd/nand/raw/qcom_nandc.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/mtd/nand/raw/qcom_nandc.c b/drivers/mtd/nand/raw/qcom_nandc.c
> index 04e6f7b26706..506006ccdf1a 100644
> --- a/drivers/mtd/nand/raw/qcom_nandc.c
> +++ b/drivers/mtd/nand/raw/qcom_nandc.c
> @@ -1459,8 +1459,7 @@ static void pre_command(struct qcom_nand_host *host, int command)
>  
>  	clear_read_regs(nandc);
>  
> -	if (command == NAND_CMD_RESET || command == NAND_CMD_READID ||
> -	    command == NAND_CMD_PARAM || command == NAND_CMD_ERASE1)
> +	if (command == NAND_CMD_RESET || command == NAND_CMD_PARAM || command == NAND_CMD_ERASE1)
>  		clear_bam_transaction(nandc);
>  }
>