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| author |   Christophe Leroy <christophe.leroy@csgroup.eu> | 2022-09-07 16:11:25 +0200 |
|---|---|---|
| committer |   Mark Brown <broonie@kernel.org> | 2022-09-07 15:18:48 +0100 |
| commit | 5e0531f6b90ac096fedaf5bd0eae0bb4e5a39da5 (patch) | |
| tree | 2bd161ccc2de94ad813dfb9cb1549140b0117043 /drivers/spi/spi.c | |
| parent | spi: nxp-fspi: Do not dereference fwnode in struct device (diff) | |
| download | linux-dev-5e0531f6b90ac096fedaf5bd0eae0bb4e5a39da5.tar.xz linux-dev-5e0531f6b90ac096fedaf5bd0eae0bb4e5a39da5.zip | |
spi: Add capability to perform some transfer with chipselect off
Some components require a few clock cycles with chipselect off before
or/and after the data transfer done with CS on.
Typically IDT 801034 QUAD PCM CODEC datasheet states "Note *: CCLK
should have one cycle before CS goes low, and two cycles after
CS goes high".
The cycles "before" are implicitely provided by all previous activity
on the SPI bus. But the cycles "after" must be provided in order to
terminate the SPI transfer.
In order to use that kind of component, add a cs_off flag to
spi_transfer struct. When this flag is set, the transfer is performed
with chipselect off. This allows consummer to add a dummy transfer
at the end of the transfer list which is performed with chipselect
OFF, providing the required additional clock cycles.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/r/434165c46f06d802690208a11e7ea2500e8da4c7.1662558898.git.christophe.leroy@csgroup.eu
Signed-off-by: Mark Brown <broonie@kernel.org>
Diffstat (limited to 'drivers/spi/spi.c')
| -rw-r--r-- | drivers/spi/spi.c | 12 |
1 files changed, 9 insertions, 3 deletions
diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c index 97487e1f27b5..c582ae4deab3 100644 --- a/drivers/spi/spi.c +++ b/drivers/spi/spi.c @@ -1435,7 +1435,8 @@ static int spi_transfer_one_message(struct spi_controller *ctlr, struct spi_statistics __percpu *statm = ctlr->pcpu_statistics; struct spi_statistics __percpu *stats = msg->spi->pcpu_statistics; - spi_set_cs(msg->spi, true, false); + xfer = list_first_entry(&msg->transfers, struct spi_transfer, transfer_list); + spi_set_cs(msg->spi, !xfer->cs_off, false); SPI_STATISTICS_INCREMENT_FIELD(statm, messages); SPI_STATISTICS_INCREMENT_FIELD(stats, messages); @@ -1503,10 +1504,15 @@ fallback_pio: &msg->transfers)) { keep_cs = true; } else { - spi_set_cs(msg->spi, false, false); + if (!xfer->cs_off) + spi_set_cs(msg->spi, false, false); _spi_transfer_cs_change_delay(msg, xfer); - spi_set_cs(msg->spi, true, false); + if (!list_next_entry(xfer, transfer_list)->cs_off) + spi_set_cs(msg->spi, true, false); } + } else if (!list_is_last(&xfer->transfer_list, &msg->transfers) && + xfer->cs_off != list_next_entry(xfer, transfer_list)->cs_off) { + spi_set_cs(msg->spi, xfer->cs_off, false); } msg->actual_length += xfer->len; |