Re: [PATCH] i3c: dw: make struct dw_i3c_cmd smaller

[Frank Li <Frank.li@oss.nxp.com>]

On Fri, Aug 14, 2026 at 11:57:24AM +0800, Jisheng Zhang wrote:
> On Thu, Aug 13, 2026 at 04:38:32PM -0400, Frank Li wrote:
> > On Thu, Aug 13, 2026 at 12:46:03PM +0800, Jisheng Zhang wrote:
> > > The dw_i3c_cmd is dynamically allocated, make it smaller. For example
> > > on 64bit platforms, we reduce the size from 48 bytes to 32 bytes.
> > >
> > > Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> > > ---
> > >  drivers/i3c/master/dw-i3c-master.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/i3c/master/dw-i3c-master.c b/drivers/i3c/master/dw-i3c-master.c
> > > index 6ba84a97765f..d6f84f0f4c2d 100644
> > > --- a/drivers/i3c/master/dw-i3c-master.c
> > > +++ b/drivers/i3c/master/dw-i3c-master.c
> > > @@ -247,10 +247,10 @@ struct dw_i3c_cmd {
> > >  	u32 cmd_lo;
> > >  	u32 cmd_hi;
> > >  	u16 tx_len;
> > > -	const void *tx_buf;
> > >  	u16 rx_len;
> >
> > only switch rx_len and tx_buf should be enough. otherwise there are data
> > pad after u8 error.
>
> If we keep the error at the end of the struct, there's still padding
> after the u8 error.
> There's no big difference between current sol and only switch rx_len and
> tx_buf on 32bit platforms. But on 64bit platforms, the current version
> makes use of the pad to store the error, thus saves 8 byte more.

Yes, I missed caculate.

Reviewed-by: Frank Li <Frank.Li@nxp.com>

>
> Thanks
> >
> > Frank
> >
> > > -	void *rx_buf;
> > >  	u8 error;
> > > +	const void *tx_buf;
> > > +	void *rx_buf;
> > >  };
> > >
> > >  struct dw_i3c_xfer {
> > > --
> > > 2.51.0
> > >