On Thu, Jun 8, 2023 at 5:08 AM William Zhang <william.zh...@broadcom.com> wrote: > > Due to the controller limitation to keep the chip select low during the > bus idle time between the transfer, a dummy cs workaround was used when > this driver was first upstreamed to the u-boot based on linux kernel > driver. It basically picks the dummy cs as !actual_cs so typically dummy > cs is 1 when most of the case only cs 0 is used in the board design. > Then invert the polarity of both cs and tell the controller to start the > transfers using dummy cs. Assuming both cs are active low before the > inversion, effectively this keeps dummy cs high and actual cs low during > the transfer and workaround the issue. > > This workaround requires that dummy cs 1 pin to is set to SPI chip > selection function in the pinmux when the transfer clock is above 25MHz. > The old chips likely have default pinmux set to chip select on the dummy > cs pin so it works but this is not case for the new Broadband BCA chips > and this workaround stop working. This is specifically an issue to > support SPI NAND and SPI NOR flash because these flash devices can > typically run at or above 100MHz. > > This patch utilizes the prepend feature of the controller to combine the > multiple transfers in the same message to a single transfer when > possible. This way there is no need to keep clock low between transfers > and solve the issue without any pinmux requirement. > > Multiple transfers within a SPI message may be combined into one > transfer if the following are all true: > * One or more half duplex write transfer in single bit mode > * Optional full duplex read/write at the end > * No delay and cs_change between transfers > > Most of the SPI device meets this requirements such as SPI NOR, SPI NAND > flash, Broadcom SPI voice card and etc. So this change switches to the > prepend mode as the default mode. For any SPI message that does not meet > the above requirement, we switch to original dummy cs mode but limit the > clock rate to the safe 25MHz. > > Port from linux patch: > Link: > https://lore.kernel.org/r/20230209200246.141520-12-william.zh...@broadcom.com > > Signed-off-by: William Zhang <william.zh...@broadcom.com> > ---
Acked-by: Jagan Teki <ja...@amarulasolutions.com> Applied to u-boot-spi/master
