RE: [PATCH V5 09/15] spi: Add stacked and parallel memories support in SPI core

Hello,

-----Original Message-----
From: Jonas Gorski <jonas.gorski@gmail.com>
Sent: Tuesday, March 7, 2023 1:31 AM
To: Mahapatra, Amit Kumar <redacted>
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Subject: Re: [PATCH V5 09/15] spi: Add stacked and parallel memories
support in SPI core

Hi,

On Mon, 6 Mar 2023 at 18:26, Amit Kumar Mahapatra <amit.kumar-
mahapatra@amd.com> wrote:

quoted

For supporting multiple CS the SPI device need to be aware of all the
CS values. So, the "chip_select" member in the spi_device structure is
now an array that holds all the CS values.

spi_device structure now has a "cs_index_mask" member. This acts as an
index to the chip_select array. If nth bit of spi->cs_index_mask is
set then the driver would assert spi->chip_select[n].

In parallel mode all the chip selects are asserted/de-asserted
simultaneously and each byte of data is stored in both devices, the
even bits in one, the odd bits in the other. The split is
automatically handled by the GQSPI controller. The GQSPI controller
supports a maximum of two flashes connected in parallel mode. A
"multi-cs-cap" flag is added in the spi controntroller data, through
ctlr->multi-cs-cap the spi core will make sure that the controller is
capable of handling multiple chip selects at once.

For supporting multiple CS via GPIO the cs_gpiod member of the
spi_device structure is now an array that holds the gpio descriptor
for each chipselect.

Multi CS support using GPIO is not tested due to unavailability of
necessary hardware setup.

Signed-off-by: Amit Kumar Mahapatra <amit.kumar-

mahapatra@amd.com>

quoted

---
 drivers/spi/spi.c       | 213 +++++++++++++++++++++++++++-------------
 include/linux/spi/spi.h |  34 +++++--
 2 files changed, 173 insertions(+), 74 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c index

5866bf5813a4..8ec7f58fa111 100644

--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c

@@ -613,7 +613,8 @@ static int spi_dev_check(struct device *dev, void

*data)

quoted

        struct spi_device *new_spi = data;

        if (spi->controller == new_spi->controller &&
-           spi_get_chipselect(spi, 0) == spi_get_chipselect(new_spi, 0))
+           spi_get_chipselect(spi, 0) == spi_get_chipselect(new_spi, 0) &&
+           spi_get_chipselect(spi, 1) == spi_get_chipselect(new_spi,
+ 1))
                return -EBUSY;

This will only reject new devices if both chip selects are identical, but not if
they only share one, e.g. CS 1 + 2 vs 1 + 3, or 1 + 2 vs only 2, or if the order is
different (1 + 2 vs 2 + 1 - haven't read the code too close to know if this is
allowed/possible).

Agreed,  will add in the next series.

Regards,
Amit

Regards,
Jonas