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rockchip: spi: only wait for completion, if transmitting

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The logic in the main transmit loop took a bit of reading the TRM to
fully understand (due to silent assumptions based in internal logic):
the "wait until idle" at the end of each iteration through the loop is
required for the transmit-path as each clearing of the ENA register
(to update run-length in the CTRLR1 register) will implicitly flush
the FIFOs... transmisson can therefore not overlap loop iterations.

This change adds a comment to clarify the reason/need for waiting
until the controller becomes idle and wraps the entire check into an
'if (out)' to make it clear that this is required for transfers with a
transmit-component only (for transfers having a receive-component,
completion of the transmit-side is trivially ensured by having
received the correct number of bytes).

The change does not increase execution time measurably in any of my
tests.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
This commit is contained in:
Philipp Tomsich 2019-02-03 16:17:30 +01:00
parent b6101e906f
commit 7e0e5c552f
1 changed files with 12 additions and 3 deletions
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15
drivers/spi/rk_spi.c
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@ -379,9 +379,18 @@ static int rockchip_spi_xfer(struct udevice *dev, unsigned int bitlen,
toread--;
}
}
ret = rkspi_wait_till_not_busy(regs);
if (ret)
break;
/*
* In case that there's a transmit-component, we need to wait
* until the control goes idle before we can disable the SPI
* control logic (as this will implictly flush the FIFOs).
*/
if (out) {
ret = rkspi_wait_till_not_busy(regs);
if (ret)
break;
}
len -= todo;
}