linux-kernel - Re: [PATCH V1 2/4] nvmem: core: introduce "reverse-data" property to reverse buffer

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Message-ID: <2a69b82c-0ecb-51cf-ea60-1827c60bfe85@linaro.org>
Date:   Wed, 11 Aug 2021 10:52:18 +0100
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Joakim Zhang <qiangqing.zhang@....com>, robh+dt@...nel.org,
        shawnguo@...nel.org
Cc:     kernel@...gutronix.de, linux-imx@....com,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V1 2/4] nvmem: core: introduce "reverse-data" property to
 reverse buffer



On 10/08/2021 08:35, Joakim Zhang wrote:
> This patch intends to introduce "reverse-data" property at nvmem
> provider side to reverse buffer.
> 
> For a case used from Ethernet driver, of_get_mac_address() may call
> of_get_mac_addr_nvmem() to get MAC address from nvmem device. MAC address
> programed in imx-ocopt is MSB first in lowest address, so need reverse

Is all the data stored in imx-ocopt reverse byte order?

or someone decided to change the order for only mac-address?


> data then feedback to nvmem consumer. E.g. MAC address read from
> imx-ocopt is 98:e2:06:9f:04:00, after reversed the data is
> 00:04:9f:06:e2:98.
> 
> Signed-off-by: Joakim Zhang <qiangqing.zhang@....com>
> ---
>   drivers/nvmem/core.c           | 30 ++++++++++++++++++++++++++++++
>   include/linux/nvmem-provider.h |  2 ++
>   2 files changed, 32 insertions(+)
> 
> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> index b3bc30a04ed7..ccc2c5801c8e 100644
> --- a/drivers/nvmem/core.c
> +++ b/drivers/nvmem/core.c
> @@ -55,6 +55,7 @@ struct nvmem_cell {
>   	struct device_node	*np;
>   	struct nvmem_device	*nvmem;
>   	struct list_head	node;
> +	u32			flags;

This flag also needs to go in struct nvmem_cell_info too.

>   };
>   
>   static DEFINE_MUTEX(nvmem_mutex);
> @@ -92,6 +93,26 @@ static int __nvmem_reg_write(struct nvmem_device *nvmem, unsigned int offset,
>   	return -EINVAL;
>   }
>   
> +static int nvmem_buffer_reverse(void *bufaddr, int len)
> +{
> +	u8 *buf = (u8 *)bufaddr;
> +	u8 *temp;
> +	int i;
> +
> +	temp = kzalloc(len, GFP_KERNEL);
> +	if (!temp)
> +		return -ENOMEM;
> +
> +	memcpy(temp, buf, len);
> +
> +	for (i = 0; i < len; i++)
> +		buf[i] = temp[len - i - 1];
> +

You could possibly simplify this.

static void nvmem_buffer_reverse(u8 *buf, int len)
{
	int i;

	for (i = 0; i < len/2; i++)
		swap(buf[i], buf[len - i - 1]);
}

> +	kfree(temp);
> +
> +	return 0;
> +}
> +
>   static int nvmem_access_with_keepouts(struct nvmem_device *nvmem,
>   				      unsigned int offset, void *val,
>   				      size_t bytes, int write)
> @@ -705,6 +726,9 @@ static int nvmem_add_cells_from_of(struct nvmem_device *nvmem)
>   		cell->bytes = be32_to_cpup(addr);
>   		cell->name = kasprintf(GFP_KERNEL, "%pOFn", child);
>   
> +		if (of_property_read_bool(child, "reverse-data"))
> +			cell->flags |= NVMEM_FLAGS_REVERSE_DATA;
> +
>   		addr = of_get_property(child, "bits", &len);
>   		if (addr && len == (2 * sizeof(u32))) {
>   			cell->bit_offset = be32_to_cpup(addr++);
> @@ -1398,6 +1422,12 @@ static int __nvmem_cell_read(struct nvmem_device *nvmem,
>   	if (cell->bit_offset || cell->nbits)
>   		nvmem_shift_read_buffer_in_place(cell, buf);
>   
> +	if (cell->flags & NVMEM_FLAGS_REVERSE_DATA) {
> +		rc = nvmem_buffer_reverse(buf, cell->bytes);
> +		if (rc < 0)
> +			return rc;
> +	}
> +
>   	if (len)
>   		*len = cell->bytes;
>   
> diff --git a/include/linux/nvmem-provider.h b/include/linux/nvmem-provider.h
> index 104505e9028f..364ac2a61b11 100644
> --- a/include/linux/nvmem-provider.h
> +++ b/include/linux/nvmem-provider.h
> @@ -31,6 +31,8 @@ enum nvmem_type {
>   #define NVMEM_DEVID_NONE	(-1)
>   #define NVMEM_DEVID_AUTO	(-2)
>   
> +#define NVMEM_FLAGS_REVERSE_DATA	BIT(0)

Maybe NVMEM_FLAGS_REVERSE_BYTE_ORDER and some kerneldoc would help new 
users.

--srini
> +
>   /**
>    * struct nvmem_keepout - NVMEM register keepout range.
>    *
>