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Date:   Fri, 12 Jun 2020 09:23:13 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Sivaprakash Murugesan <sivaprak@...eaurora.org>
Cc:     richard@....at, vigneshr@...com, peter.ujfalusi@...com,
        boris.brezillon@...labora.com, architt@...eaurora.org,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 2/2] mtd: rawnand: qcom: set BAM mode only if not set
 already

Hi Sivaprakash,

Sivaprakash Murugesan <sivaprak@...eaurora.org> wrote on Fri, 12 Jun
2020 12:19:49 +0530:

> BAM is DMA controller on QCOM ipq platforms, BAM mode on NAND driver
> 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

So, before enabling BAM mode by writing the NAND_CTRL register, check
if BAM mode was already enabled by the bootloader.

> enabled by bootloader, and set BAM mode only if it is not set already.
> 
> Signed-off-by: Sivaprakash Murugesan <sivaprak@...eaurora.org>
> ---
> [V3]
>  * Changed commit message to give a small info about BAM
>  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 e0c55bb..4827edd 100644
> --- a/drivers/mtd/nand/raw/qcom_nandc.c
> +++ b/drivers/mtd/nand/raw/qcom_nandc.c
> @@ -2784,7 +2784,14 @@ 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

                                        BAM mode already (Bootloaders
                                        might have already entered
                                        this mode).

> +		 * 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);
>  	}

Thanks,
Miquèl

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