linux-kernel - Re: [PATCH v2 1/3] i3c: master: Add inline i3c_readl_fifo() and i3c_writel

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Message-ID: <aFl2F+AEa6S1iA/h@lizhi-Precision-Tower-5810>
Date: Mon, 23 Jun 2025 11:43:19 -0400
From: Frank Li <Frank.li@....com>
To: Jorge Marques <jorge.marques@...log.com>
Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>,
	Przemysław Gaj <pgaj@...ence.com>,
	linux-i3c@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] i3c: master: Add inline i3c_readl_fifo() and
 i3c_writel_fifo()

On Sun, Jun 22, 2025 at 11:18:58AM +0200, Jorge Marques wrote:
> The i3c abstraction excepts u8 buffers, but some controllers have a bus
                      ^ expects?

> width of 32-bits and don't support flagging valid bytes, so it is
> required to read/write long words and to use memcpy on the remainder of
> the number of bytes by 32-bits to not write/read outside the buffer
> bounds.

The I3C abstraction expects u8 buffers, but some controllers operate with
a 32-bit bus width FIFO and cannot flag valid bytes individually. To avoid
reading or writing outside the buffer bounds, use 32-bit accesses where
possible and apply memcpy for any remaining bytes.

Frank
>
> Signed-off-by: Jorge Marques <jorge.marques@...log.com>
> ---
>  drivers/i3c/internals.h | 37 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 37 insertions(+)
>
> diff --git a/drivers/i3c/internals.h b/drivers/i3c/internals.h
> index 433f6088b7cec8c77288ee24dbee8b18338aa1eb..88887b12122efafac81bcfdd093d943259e13a08 100644
> --- a/drivers/i3c/internals.h
> +++ b/drivers/i3c/internals.h
> @@ -22,4 +22,41 @@ int i3c_dev_enable_ibi_locked(struct i3c_dev_desc *dev);
>  int i3c_dev_request_ibi_locked(struct i3c_dev_desc *dev,
>  			       const struct i3c_ibi_setup *req);
>  void i3c_dev_free_ibi_locked(struct i3c_dev_desc *dev);
> +
> +/**
> + * i3c_master_writesl- Write bytes to long memory region from byte array

i3c_writel_fifo - Write data buffer to 32bit FIFO

> + * @addr: Register to write to

FIFO address

> + * @bytes: Pointer to the data bytes to write

bytes and nbytes is too similar, can you rename bytes to buf?

Check read_fifo also.

Frank
> + * @nbytes: Number of bytes to write
> + */
> +static inline void i3c_writel_fifo(void __iomem *addr, const void *bytes,
> +				   int nbytes)
> +{
> +	writesl(addr, bytes, nbytes / 4);
> +	if (nbytes & 3) {
> +		u32 tmp = 0;
> +
> +		memcpy(&tmp, bytes + (nbytes & ~3), nbytes & 3);
> +		writel(tmp, addr);
> +	}
> +}
> +
> +/**
> + * i3c_master_readsl - Read bytes from long memory region to byte array
> + * @addr: Register to read from
> + * @bytes: Pointer to the buffer to store read bytes
> + * @nbytes: Number of bytes to read
> + */
> +static inline void i3c_readl_fifo(const void __iomem *addr, void *bytes,
> +				  int nbytes)
> +{
> +	readsl(addr, bytes, nbytes / 4);
> +	if (nbytes & 3) {
> +		u32 tmp;
> +
> +		tmp = readl(addr);
> +		memcpy(bytes + (nbytes & ~3), &tmp, nbytes & 3);
> +	}
> +}
> +
>  #endif /* I3C_INTERNAL_H */
>
> --
> 2.49.0
>
>