Hi Geert, On Thu, Jul 10, 2014 at 4:55 PM, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: > Hi Harini, > > On Thu, Jul 10, 2014 at 12:33 PM, Harini Katakam > <harinikatakamlinux@xxxxxxxxx> wrote: >> On Thu, Jul 10, 2014 at 3:12 PM, Geert Uytterhoeven >> <geert@xxxxxxxxxxxxxx> wrote: >>> On Thu, Jul 10, 2014 at 11:31 AM, Harini Katakam >>> <harinikatakamlinux@xxxxxxxxx> wrote: >>>>>> + master->mode_bits = SPI_CPOL | SPI_CPHA | SPI_RX_DUAL | SPI_RX_QUAD | >>>>>> + SPI_TX_DUAL | SPI_TX_QUAD; >>>>> >>>>> Your driver advertises Dual/Quad SPI Transfer capabilities, but it doesn't >>>>> check spi_transfer.[tr]x_nbits? How can it determine when to enable Dual/Quad? >>>> >>>> Here the driver is just giving information that the controller support it. >>>> The MTD layer enables dual/quad based on what the flash supports; quad >>>> being the first priority >>>> I understand that the spi core reads rx, tx-bus-width property and >>>> master support flags and >>>> performs the necessary checks. >>> >>> That's correct: as long as the rx, tx-bus-width properties do not indicate a >>> Dual or Quad wiring, it won't be used. >>> >>> However, based on schematics, someone may set the rx, tx-bus-width properties >>> to 4, which is correct, as DT describes the hardware. But this will fail to >>> work. >>> So I think it's safer not to announce Dual/Quad support in the driver until >>> the actual driver support is there. >> >> OK. Correct me if I'm wrong but announcing this support in master->flags is >> just to say the controller supports it - Like Punnaiah mentioned in the other >> mail, nothing specific needs to be done from the controller driver to enable >> dual/quad support. This is at the SOC/IP level. >> I agree it might or might not be supported at board-level. > > IC. So this is not a generic SPI controller, but a controller meant for QSPI > FLASHes? I.e. if you would connect a different device, the controller may > unexpectedly use Dual or Quad mode if it sees a byte fly by that looks like > a Quad SPI FLASH read command? > Yes. It would. >> But that's based on the user's hardware. Should master->flags >> really take this into consideration? > > You mean master->mode_bits? Yes, i mean mode_bits. That was typo. > >> BTW, I dint see master->mode_bits being used anywhere at the moment. > > It is used to match SPI controller and slave features, cfr. spi_setup() in > drivers/spi/spi.c. > > If Dual/Quad is supported, the bits should be set. Else spi_setup() will > clear the bits in the SPI slave's mode field, disabling Dual/Quad transfers. > OK. Regards, Harini -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
