Re: [PATCH v5 07/10] i3c: master: Add driver for Cadence IP

[Arnd Bergmann <arnd@arndb.de>]

On Fri, Jun 22, 2018 at 12:49 PM, Boris Brezillon
<boris.brezillon@bootlin.com> wrote:
> Add a driver for Cadence I3C master IP.

The driver seems very well-written and shows that the framework got that side
of the interface right. Just one thing I noticed:

> +
> +static void cdns_i3c_master_handle_ibi(struct cdns_i3c_master *master,
> +                                      u32 ibir)

> +
> +       for (i = 0; i < IBIR_XFER_BYTES(ibir); i += 4) {
> +               u32 tmp = readl(master->regs + IBI_DATA_FIFO);
> +
> +               for (j = 0; j < 4 && i + j < dev->ibi->max_payload_len; j++)
> +                       buf[i + j] = tmp >> (j * 8);
> +       }

This seems to be a rather inefficient way to open-code a readsl().
I suppose you need to handle length that is not a multiple of 4, right?

Maybe do it like

      size_t length = IBIR_XFER_BYTES(ibir);
      readsl(master->regs + IBI_DATA_FIFO, buf, length & ~3);
      if (length & 3) {
            u32 tmp = __raw_readl(master->regs + IBI_DATA_FIFO);
            memcpy(buf + length & ~3, length & 3);
      }

     Arnd