From: Bjorn Andersson <bjorn.andersson@linaro.org>
To: Douglas Anderson <dianders@chromium.org>
Cc: Mark Brown <broonie@kernel.org>,
Akash Asthana <akashast@codeaurora.org>,
swboyd@chromium.org, Andy Gross <agross@kernel.org>,
linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-spi@vger.kernel.org
Subject: Re: [PATCH 3/3] spi: spi-geni-qcom: Slightly optimize setup of bidirectional xfters
Date: Sat, 12 Sep 2020 17:54:40 -0500 [thread overview]
Message-ID: <20200912225440.GB3715@yoga> (raw)
In-Reply-To: <20200912140730.3.Ided778fb4cd078e36c6b240d1b279cd7a534a313@changeid>
On Sat 12 Sep 16:08 CDT 2020, Douglas Anderson wrote:
> When setting up a bidirectional transfer we need to program both the
> TX and RX lengths. We don't need a memory barrier between those two
> writes. Factor out the __iowmb() and use writel_relaxed(). This
> saves a fraction of a microsecond of setup overhead on bidirectional
> transfers.
>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
>
> drivers/spi/spi-geni-qcom.c | 13 ++++++++++---
> 1 file changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/spi/spi-geni-qcom.c b/drivers/spi/spi-geni-qcom.c
> index 92d88bf85a90..6c7e12b68bf0 100644
> --- a/drivers/spi/spi-geni-qcom.c
> +++ b/drivers/spi/spi-geni-qcom.c
> @@ -376,15 +376,22 @@ static void setup_fifo_xfer(struct spi_transfer *xfer,
> len &= TRANS_LEN_MSK;
>
> mas->cur_xfer = xfer;
> +
> + /*
> + * Factor out the __iowmb() so that we can use writel_relaxed() for
> + * both writes below and thus only incur the overhead once even if
> + * we execute both of them.
> + */
How many passes through this function do we have to take before saving
the amount of time it took me to read this comment?
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Regards,
Bjorn
> + __iowmb();
> +
> if (xfer->tx_buf) {
> m_cmd |= SPI_TX_ONLY;
> mas->tx_rem_bytes = xfer->len;
> - writel(len, se->base + SE_SPI_TX_TRANS_LEN);
> + writel_relaxed(len, se->base + SE_SPI_TX_TRANS_LEN);
> }
> -
> if (xfer->rx_buf) {
> m_cmd |= SPI_RX_ONLY;
> - writel(len, se->base + SE_SPI_RX_TRANS_LEN);
> + writel_relaxed(len, se->base + SE_SPI_RX_TRANS_LEN);
> mas->rx_rem_bytes = xfer->len;
> }
>
> --
> 2.28.0.618.gf4bc123cb7-goog
>
next prev parent reply other threads:[~2020-09-12 22:54 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-12 21:07 [PATCH 1/3] spi: spi-geni-qcom: Use the FIFO even more Douglas Anderson
2020-09-12 21:08 ` [PATCH 2/3] spi: spi-geni-qcom: Don't program CS_TOGGLE again and again Douglas Anderson
2020-09-12 23:01 ` Bjorn Andersson
2020-09-15 10:40 ` Akash Asthana
2020-09-12 21:08 ` [PATCH 3/3] spi: spi-geni-qcom: Slightly optimize setup of bidirectional xfters Douglas Anderson
2020-09-12 22:54 ` Bjorn Andersson [this message]
2020-09-13 1:09 ` Doug Anderson
2020-09-13 20:35 ` Doug Anderson
2020-09-13 3:45 ` kernel test robot
2020-09-13 7:31 ` kernel test robot
2020-09-12 22:53 ` [PATCH 1/3] spi: spi-geni-qcom: Use the FIFO even more Bjorn Andersson
2020-09-13 1:11 ` Doug Anderson
2020-09-13 3:12 ` Bjorn Andersson
2020-09-14 14:52 ` Mark Brown
2020-09-15 7:30 ` Akash Asthana
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