linux-kernel - Re: [PATCH V2 1/2] mtd: rawnand: qcom: remove write to unavailable register

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Date:   Tue, 9 Jun 2020 16:02:17 +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 1/2] mtd: rawnand: qcom: remove write to unavailable
 register

Hi Sivaprakash,

Sivaprakash Murugesan <sivaprak@...eaurora.org> wrote on Tue,  9 Jun
2020 16:40:55 +0530:

> SFLASHC_BURST_CFG register is not available on all ipq nand platforms,
> it is available only on ipq8064 devices and the nand controller works
> without configuring these registers in this platform, so register write
> to this can be removed.

Maybe it works because the bootloader is setting the register itself.
What if you use a different bootloader, or the same bootloader without
NAND support?

I don't think this is a proper fix, you should instead have a different
compatible if the IP is not the same and depending on this compatible
do the write, or not.

> 
> Signed-off-by: Sivaprakash Murugesan <sivaprak@...eaurora.org>
> ---
>  drivers/mtd/nand/raw/qcom_nandc.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/mtd/nand/raw/qcom_nandc.c b/drivers/mtd/nand/raw/qcom_nandc.c
> index 5b11c70..e0afa2c 100644
> --- a/drivers/mtd/nand/raw/qcom_nandc.c
> +++ b/drivers/mtd/nand/raw/qcom_nandc.c
> @@ -36,7 +36,6 @@
>  #define	NAND_DEV_CMD1			0xa4
>  #define	NAND_DEV_CMD2			0xa8
>  #define	NAND_DEV_CMD_VLD		0xac
> -#define	SFLASHC_BURST_CFG		0xe0
>  #define	NAND_ERASED_CW_DETECT_CFG	0xe8
>  #define	NAND_ERASED_CW_DETECT_STATUS	0xec
>  #define	NAND_EBI2_ECC_BUF_CFG		0xf0
> @@ -2774,7 +2773,6 @@ static int qcom_nandc_setup(struct qcom_nand_controller *nandc)
>  	u32 nand_ctrl;
>  
>  	/* kill onenand */
> -	nandc_write(nandc, SFLASHC_BURST_CFG, 0);
>  	nandc_write(nandc, dev_cmd_reg_addr(nandc, NAND_DEV_CMD_VLD),
>  		    NAND_DEV_CMD_VLD_VAL);
>  

Thanks,
Miquèl