Messages in this thread | | | Date | Thu, 9 Mar 2023 12:42:35 +0200 | Subject | Re: [PATCH] spi: Replace `dummy.nbytes` with `dummy.ncycles` | From | Tudor Ambarus <> |
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On 09.03.2023 10:38, Michael Walle wrote: >> In an ideal world, where both the controller and the device talk about >> dummy number of cycles, I would agree with you, buswidth and dtr should >> not be relevant for the number of dummy cycles. But it seems that there >> are old controllers (e.g. spi-hisi-sfc-v3xx.c, spi-mt65xx.c, spi-mxic.c) >> that support buswidths > 1 and work only with dummy nbytes, they are not >> capable of specifying a smaller granularity (ncycles). Thus the older >> controllers would have to convert the dummy ncycles to dummy nbytes. >> Since mixed transfer modes are a thing (see jesd251, it talks about >> 4S-4D-4D), where single transfer mode (S) can be mixed with double >> transfer mode (D) for a command, the controller would have to guess the >> buswidth and dtr of the dummy. Shall they replicate the buswidth and dtr >> of the address or of the data? There's no rule for that. > > But in the end that doesn't matter because they are just dummy clock > cycles and the mode will only affect the data/address/command. Therefore, > the controller is free to choose the mode that suits it best. > > But that begs the question, is ncycles in regard to DTR or SDR? That is, > are you counting just one type of edges or both the falling and rising > edges. The smallest granularity would be ncycles in regard of DTR. To me, > it's not obvious what the SEMPER Nano Flash [1] uses. I'd say we choose > the smallest granularty in spi-mem to be future proof and maybe provide > some spi-mem helper to help setting the cycles for SDR/DTR. As an example, > if you want to wait 4 cycles in SDR you'd have ncycles=8 in spi-mem. >
No, we can't invent our own measuring units. We have cycles and half cycles (regardless of the transfer mode used (STR, DTR)).
> So you won't need the mode nor the dtr property. > > -michael > > [1] > https://www.infineon.com/dgdl/Infineon-S25FS256T_256Mb_SEMPER_Nano_Flash_Quad_SPI_1.8V-DataSheet-v01_00-EN.pdf?fileId=8ac78c8c80027ecd0180740c5a46707a
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