Performance of spi_mpc83xx.c sucks.

["Joakim Tjernlund" <joakim.tjernlund-SNLAxHN9vbcOP4wsBPIw7w@public.gmane.org>]

We have noticed that the spi_mpc83xx.c driver is very slow, the gap
between words are huge.
So I started to optimise it and it still sucks.
However, if I poll the SPIE_NF SPIE_NE bits instead it works MUCH
better, like so:
		struct mpc83xx_spi_reg *regs = mpc83xx_spi->base;
		u32 event=SPIE_NF;

		mpc83xx_spi->tx_count -= 1;
		word = mpc83xx_spi->get_tx(mpc83xx_spi);
		mpc83xx_spi_write_reg(&regs->transmit, word);
		if (len >= 2) { /* FIFO is 2 words */
			mpc83xx_spi->tx_count -= 1;
			word = mpc83xx_spi->get_tx(mpc83xx_spi);
			mpc83xx_spi_write_reg(&regs->transmit, word);
		}
		clear_need_resched();
		do {
			if (event & SPIE_NE) {
				word = mpc83xx_spi_read_reg(&regs->receive);
				mpc83xx_spi->rx_count -= 1;
				if (mpc83xx_spi->rx)
					mpc83xx_spi->get_rx(word, mpc83xx_spi);

				if ((event & SPIE_NF) && mpc83xx_spi->tx_count) {
					mpc83xx_spi->tx_count -= 1;
					word = mpc83xx_spi->get_tx(mpc83xx_spi);
					mpc83xx_spi_write_reg(&regs->transmit, word);
				}

			} else if (need_resched()){
				clear_need_resched();
				schedule();
				printk("Cond, rx:%d\n", mpc83xx_spi->rx_count);
			}

			event = mpc83xx_spi_read_reg(&regs->event);
			} while (mpc83xx_spi->rx_count);

I am not sure what this polling will do to the system though. Is this really bad to do?
The resched() stuff doesn't seem to work, probably becase I don't know how
to use it properly :(

 Jocke



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