Re: [PATCH 1/4] nvmem: sunxi_sid: Always use 32-bit MMIO reads

[Srinivas Kandagatla]

On 14/08/2022 18:36, Samuel Holland wrote:
> The SID SRAM on at least some SoCs (A64 and D1) returns different values
> when read with bus cycles narrower than 32 bits. This is not immediately
> obvious, because memcpy_fromio() uses word-size accesses as long as
> enough data is being copied.
>
> The vendor driver always uses 32-bit MMIO reads, so do the same here.
> This is faster than the register-based method, which is currently used
> as a workaround on A64. And it fixes the values returned on D1, where
> the SRAM method was being used.
>
> The special case for the last word is needed to maintain .word_size == 1
> for sysfs ABI compatibility, as noted previously in commit de2a3eaea552
> ("nvmem: sunxi_sid: Optimize register read-out method").
Missing Cc stable..

--srini
> Fixes: 07ae4fde9efa ("nvmem: sunxi_sid: Add support for D1 variant")
> Signed-off-by: Samuel Holland <samuel@xxxxxxxxxxxx>
> ---
>
>   drivers/nvmem/sunxi_sid.c | 15 ++++++++++++++-
>   1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/nvmem/sunxi_sid.c b/drivers/nvmem/sunxi_sid.c
> index 5750e1f4bcdb..92dfe4cb10e3 100644
> --- a/drivers/nvmem/sunxi_sid.c
> +++ b/drivers/nvmem/sunxi_sid.c
> @@ -41,8 +41,21 @@ static int sunxi_sid_read(void *context, unsigned int offset,
>   			  void *val, size_t bytes)
>   {
>   	struct sunxi_sid *sid = context;
> +	u32 word;
> +
> +	/* .stride = 4 so offset is guaranteed to be aligned */
> +	__ioread32_copy(val, sid->base + sid->value_offset + offset, bytes / 4);
>   
> -	memcpy_fromio(val, sid->base + sid->value_offset + offset, bytes);
> +	val += round_down(bytes, 4);
> +	offset += round_down(bytes, 4);
> +	bytes = bytes % 4;
> +
> +	if (!bytes)
> +		return 0;
> +
> +	/* Handle any trailing bytes */
> +	word = readl_relaxed(sid->base + sid->value_offset + offset);
> +	memcpy(val, &word, bytes);
>   
>   	return 0;
>   }