linux-kernel - Re: [PATCH V2 2/2] mtd: rawnand: qcom: set BAM mode only if not set already

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Message-ID: <20200609160352.60cbad80@xps13>
Date:   Tue, 9 Jun 2020 16:03:52 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Sivaprakash Murugesan <sivaprak@...eaurora.org>
Cc:     richard@....at, vigneshr@...com, peter.ujfalusi@...com,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 2/2] mtd: rawnand: qcom: set BAM mode only if not set
 already

Hi Sivaprakash,

Sivaprakash Murugesan <sivaprak@...eaurora.org> wrote on Tue,  9 Jun
2020 16:40:56 +0530:

> BAM mode is set by writing BAM_MODE_EN bit on NAND_CTRL register.
> NAND_CTRL is an operational register and in BAM mode operational
> registers are read only.
> 
> So, before writing into NAND_CTRL register check if BAM mode is already
> enabled by bootloader, and set BAM mode only if it is not set already.
> 
> Signed-off-by: Sivaprakash Murugesan <sivaprak@...eaurora.org>
> ---
>  drivers/mtd/nand/raw/qcom_nandc.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/nand/raw/qcom_nandc.c b/drivers/mtd/nand/raw/qcom_nandc.c
> index e0afa2c..7740059 100644
> --- a/drivers/mtd/nand/raw/qcom_nandc.c
> +++ b/drivers/mtd/nand/raw/qcom_nandc.c
> @@ -2779,7 +2779,14 @@ static int qcom_nandc_setup(struct qcom_nand_controller *nandc)
>  	/* enable ADM or BAM DMA */
>  	if (nandc->props->is_bam) {
>  		nand_ctrl = nandc_read(nandc, NAND_CTRL);
> -		nandc_write(nandc, NAND_CTRL, nand_ctrl | BAM_MODE_EN);
> +		/* NAND_CTRL is an operational registers, and CPU
> +		 * access to operational registers are read only
> +		 * in BAM mode. So update the NAND_CTRL register
> +		 * only if it is not in BAM mode. In most cases BAM
> +		 * mode will be enabled in bootloader
> +		 */
> +		if (!(nand_ctrl | BAM_MODE_EN))
> +			nandc_write(nandc, NAND_CTRL, nand_ctrl | BAM_MODE_EN);
>  	} else {
>  		nandc_write(nandc, NAND_FLASH_CHIP_SELECT, DM_EN);
>  	}

Does this currently produces an issue at runtime?

If yes, you should have a Fixes/CC: stable pair of tags.

Also, what is BAM mode? Please tell us in the commit log.

Thanks,
Miquèl