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

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Message-ID: <kkbswsflgmfl2khbtwnlsntyzpublt666ozgv7snw4sbv2oteh@ry4wvwkz7uxz>
Date: Tue, 24 Jun 2025 10:50:15 +0200
From: Jorge Marques <gastmaier@...il.com>
To: Frank Li <Frank.li@....com>
Cc: Jorge Marques <jorge.marques@...log.com>, 
	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 Mon, Jun 23, 2025 at 11:43:19AM -0400, Frank Li wrote:
> 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.
Hi Frank,

gotcha,
> 
> 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?
Yep
> 
> Check read_fifo also.
Ack
> 
> Frank

Regards,
Jorge
> > + * @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
> >
> >