Re: [PATCH RFC 2/2] staging: fbtft: fix 9-bit SPI support detection

From: Noralf TrÃnnes
Date: Tue Aug 25 2015 - 14:21:43 EST

Den 25.08.2015 19:34, skrev Stefan Wahren:
Noralf TrÃnnes <noralf@xxxxxxxxxxx> hat am 25. August 2015 um 00:00

Den 24.08.2015 20:33, skrev Stefan Wahren:
Since bits_per_word isn't usually checked during SPI setup the 9-bit
support must be checked manually.

Signed-off-by: Stefan Wahren <stefan.wahren@xxxxxxxx>
drivers/staging/fbtft/fbtft-core.c | 7 +++++++
drivers/staging/fbtft/flexfb.c | 7 +++++++
2 files changed, 14 insertions(+)

diff --git a/drivers/staging/fbtft/fbtft-core.c
index 3638554..bd71487 100644
--- a/drivers/staging/fbtft/fbtft-core.c
+++ b/drivers/staging/fbtft/fbtft-core.c
@@ -1438,6 +1438,13 @@ int fbtft_probe_common(struct fbtft_display *display,
if (par->spi && display->buswidth == 9) {
par->spi->bits_per_word = 9;
ret = spi_setup(par->spi);
+ if (!ret) {
+ struct spi_master *ma = par->spi->master;
+ if (!(ma->bits_per_word_mask & SPI_BPW_MASK(9)))
+ ret = -EINVAL;
+ }
if (ret) {
There's no point in calling spi_setup() when it doesn't check bits_per_word.
If checking of bits_per_word is the only intention of the setup call, then i
But i'm not sure it is safe to remove the setup call complete.

Couldn't this cause regressions since there is no common spi setup call for all

spi_add_device() calls spi_setup() for all spi devices so it's already done.
If spi_setup() did something with bits_per_word, then I agree that we should
call it in the 9-bit case. But this is not the case, and it's possible to
change bits_per_word per transfer later, so I can't see that this is needed.

Apparently this changed with the commit:
spi: convert drivers to use bits_per_word_mask.
This has not been detected earlier, because FBTFT was previously mostly
used on the Raspberry Pi which had a downstream SPI driver that did this

How about this:

- par->spi->bits_per_word = 9;
- ret = par->spi->master->setup(par->spi);
+ if (par->spi->master->bits_per_word_mask &
+ par->spi->bits_per_word = 9;
- if (ret) {
+ } else {
"9-bit SPI not available, emulating
using 8-bit.\n");
- par->spi->bits_per_word = 8;
I think this assignment should stay.

Not needed since we haven't changed the default set by spi_setup():
if (!spi->bits_per_word)
spi->bits_per_word = 8;

Callchain for DT registered spi devices:

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