Hi Ashok,
Am 18.04.2023 um 10:43 schrieb Soma, Ashok Reddy:
-----Original Message----- From: Simek, Michal michal.simek@amd.com Sent: Monday, April 17, 2023 3:47 PM To: Stefan Herbrechtsmeier stefan.herbrechtsmeier-oss@weidmueller.com; u-boot@lists.denx.de; Soma, Ashok Reddy ashok.reddy.soma@amd.com Cc: Stefan Herbrechtsmeier stefan.herbrechtsmeier@weidmueller.com; Jagan Teki jagan@amarulasolutions.com Subject: Re: [PATCH] Revert "spi: zynq_qspi: Use dummy buswidth in dummy byte calculation"
On 3/31/23 16:44, Stefan Herbrechtsmeier wrote:
From: Stefan Herbrechtsmeier stefan.herbrechtsmeier@weidmueller.com
This reverts commit e09784728689de7949d4cdd559a9590e0bfcc702. The commit wrongly divides the dummy bytes by dummy bus width to calculate the dummy bytes. The framework already converts the dummy cycles to the number of bytes and the controller use the SPI flash command to determine the dummy cycles via the address width.
As per my understanding dummy bus width should be equal to data buswidth and not equal to address bus width. Please let me know if this understanding in incorrect.
Why? The kernel use the addr bus width too.
Independent of the correct answer the core should handle this because it forward the dummy *bytes* to the driver:
/* convert the dummy cycles to the number of bytes */ op.dummy.nbytes = (nor->read_dummy * op.dummy.buswidth) / 8;
Furthermore, the driver send the dummy as part of the address:
/* 1st transfer: opcode + address + dummy cycles */
Based on the above understanding we have changed in Xilinx repo, at below code https://github.com/Xilinx/u-boot-xlnx/blob/024eb37c1e38ab811abe5408d42069fbd... from op->dummy.buswidth = spi_nor_get_protocol_addr_nbits(proto); to op->dummy.buswidth = spi_nor_get_protocol_data_nbits(proto);
I have sent the same as RFC. Please see the attached patch.
Currently this patch is present as part of Xilinx repo, and hence based on this below implementation dymmy_bytes are recalculated.
In this case the patch should be reverted until the other patch is accepted.
I have sent controller driver code to upstream but, I have not yet sent spi-nor-core.c code, which I will be sending soon with some other changes.
Please let me know your thoughts about this patch and the changes.
It is unclear to me why the dummy should be part of the data. The current implementation is wrong because it doesn't respects the address width and send the dummy bytes as part of the addr.
Regards Stefan
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