[PATCH 02/30] mtd: spi-nor-core: Set dummy buswidth equal to data buswidth

[Stefan Herbrechtsmeier]

Hi Tejas Bhumkar,

Am 06.12.2023 um 06:30 schrieb Tejas Bhumkar:
> From: T Karthik Reddy <t.karthik.reddy at xilinx.com>
>
> In current implementation dummy buswidth is set equal to address
> buswidth. In case of quad spi (mode 1-1-4), where address width is 1
> the dummy bytes will be calculated to 1(8 dummy cycles) and dummy
> buswidth is set to 1. Due to this, the controller driver will introduce
> 8 dummy cycles on data line(D0) during read operation.
>
> But since we are using 4 data lines in case of qspi, we need to change
> this dummy bus width to 4. This will make dummy bytes to 4 inplace of 1.
> This will be taken care in controller driver by dividing with dummy
> buswidth again as in below code, which makes dummy cycles to 8 as
> earlier.

Do you have any specification that states that the dummy lines use the 
data and not the address width?

Both u-boot and the Linux kernel use the address width for the 
calculation of the dummy bytes until now.


> dummy_cycles = op->dummy.nbytes * 8 / op->dummy.buswidth;
>
> So with this change dummy cycles will be on all data lines(D0-D3) and it
> is taken care for all the configurations(single, dual, quad and octal).
>
> Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma at xilinx.com>
> Signed-off-by: T Karthik Reddy <t.karthik.reddy at xilinx.com>
> Signed-off-by: Tejas Bhumkar <tejas.arvind.bhumkar at amd.com>
> ---
>   drivers/mtd/spi/spi-nor-core.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/mtd/spi/spi-nor-core.c b/drivers/mtd/spi/spi-nor-core.c
> index 473d9f41f3..8949dab548 100644
> --- a/drivers/mtd/spi/spi-nor-core.c
> +++ b/drivers/mtd/spi/spi-nor-core.c
> @@ -260,7 +260,7 @@ void spi_nor_setup_op(const struct spi_nor *nor,
>   		op->addr.buswidth = spi_nor_get_protocol_addr_nbits(proto);
>   
>   	if (op->dummy.nbytes)
> -		op->dummy.buswidth = spi_nor_get_protocol_addr_nbits(proto);
> +		op->dummy.buswidth = spi_nor_get_protocol_data_nbits(proto);
>   
>   	if (op->data.nbytes)
>   		op->data.buswidth = spi_nor_get_protocol_data_nbits(proto);