From: Stephen Boyd <swboyd@chromium.org>
To: Douglas Anderson <dianders@chromium.org>,
Mark Brown <broonie@kernel.org>
Cc: msavaliy@qti.qualcomm.com, akashast@codeaurora.org,
Roja Rani Yarubandi <rojay@codeaurora.org>,
Douglas Anderson <dianders@chromium.org>,
Andy Gross <agross@kernel.org>,
Bjorn Andersson <bjorn.andersson@linaro.org>,
linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-spi@vger.kernel.org
Subject: Re: [PATCH v3 3/4] spi: spi-geni-qcom: Don't try to set CS if an xfer is pending
Date: Thu, 17 Dec 2020 18:54:23 -0800 [thread overview]
Message-ID: <160826006320.1580929.12847315427212664109@swboyd.mtv.corp.google.com> (raw)
In-Reply-To: <20201217142842.v3.3.I07afdedcc49655c5d26880f8df9170aac5792378@changeid>
Quoting Douglas Anderson (2020-12-17 14:29:13)
> If we get a timeout sending then this happens:
>
> spi_transfer_one_message()
> ->transfer_one() AKA spi_geni_transfer_one()
> setup_fifo_xfer()
> mas->cur_xfer = non-NULL
> spi_transfer_wait() => TIMES OUT
> if (msg->status != -EINPROGRESS)
> goto out
> if (ret != 0 ...)
> spi_set_cs()
> ->set_cs AKA spi_geni_set_cs()
> # mas->cur_xfer is non-NULL
>
> The above happens _before_ the SPI core calls ->handle_err() AKA
> handle_fifo_timeout().
>
> Unfortunately that won't work so well on geni. If we got a timeout
> transferring then it's likely that our interrupt handler is blocked,
> but we need that same interrupt handler to run and the command channel
> to be unblocked in order to adjust the chip select. Trying to set the
> chip select doesn't crash us but ends up confusing our state machine
> and leads to messages like: Premature done. rx_rem = 32 bpw8
>
> Let's just drop the chip select request in this case. We can detect
> the case because cur_xfer is non-NULL--it would have been set to NULL
> in the interrupt handler if the previous transfer had finished. Sure,
> we might leave the chip select in the wrong state but it's likely it
> was going to fail anyway and this avoids getting the driver even more
> confused about what it's doing.
>
> The SPI core in general assumes that setting chip select is a simple
> operation that doesn't fail. Yet another reason to just reconfigure
> the chip select line as GPIOs.
>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
next prev parent reply other threads:[~2020-12-18 2:55 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-17 22:29 [PATCH v3 1/4] spi: spi-geni-qcom: Fix geni_spi_isr() NULL dereference in timeout case Douglas Anderson
2020-12-17 22:29 ` [PATCH v3 2/4] spi: spi-geni-qcom: Fail new xfers if xfer/cancel/abort pending Douglas Anderson
2020-12-18 2:54 ` Stephen Boyd
2020-12-17 22:29 ` [PATCH v3 3/4] spi: spi-geni-qcom: Don't try to set CS if an xfer is pending Douglas Anderson
2020-12-18 2:54 ` Stephen Boyd [this message]
2020-12-17 22:29 ` [PATCH v3 4/4] spi: spi-geni-qcom: Print an error when we timeout setting the CS Douglas Anderson
2020-12-18 2:54 ` Stephen Boyd
2020-12-18 18:29 ` [PATCH v3 1/4] spi: spi-geni-qcom: Fix geni_spi_isr() NULL dereference in timeout case Mark Brown
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