Messages in this thread | | | Date | Mon, 1 Jun 2015 08:49:22 -0500 | From | Graham Moore <> | Subject | Re: [PATCH V4 2/2] mtd: spi-nor: Add driver for Cadence Quad SPI Flash Controller. |
| |
On 05/20/2015 05:26 PM, Brian Norris wrote: > On Mon, Mar 23, 2015 at 08:36:22AM -0500, Graham Moore wrote: ... I'm fixing the sparse, smatch, unused variables, etc. ... >> + if (n_tx && opcode == SPINOR_OP_WD_EVCR && >> + !(txbuf[0] & EVCR_QUAD_EN_MICRON)) { >> + struct cqspi_flash_pdata *f_pdata; >> + >> + f_pdata = &cqspi->f_pdata[cqspi->current_cs]; >> + f_pdata->quad_mode_set = 1; > > No, please don't do this. The whole point of the spi-nor layer is that > we don't want low-level drivers having to snoop every type of flash > command. We want to have proper feedback between spi-nor.c and your > driver, so you *know* when you're using a quad-enabled device. > > Food for thought: what happens for a non-Micron SPI flash that uses quad > mode? > > Is it sufficient to just check if nor->flash_read == SPI_NOR_QUAD? >
I *said* it was ugly :)
Here's the deal. The Cadence controller has its own quad mode setting, which must match the setting of the chip (or the quad-mode command.) Before the addition of micron_quad_enable(), spi-nor was using a quad-mode read command. That was all good, because we could use nor->flash_read == SPI_NOR_QUAD to set the Cadence controller properly.
However, micron_quad_enable() sets quad mode in the Micron chip. At that point, all communication with the chip must be in quad mode, even the very next read-status command. The micron_quad_enable() function reads status and EVCR register to see if the quad-mode command 'took'. This all happens before nor->flash_read is set to SPI_NOR_QUAD. If I don't set the Cadence controller into quad mode immediately after the chip is set into quad mode, then status is garbage and the probe fails.
I agree that any other chip with a quad mode, separate from quad commands, will be jacked up too.
So...how can I know when to set the Cadence controller into quad mode? Perhaps the micron_quad_enable() should set nor->flash_read = SPI_NOR_QUAD as soon as it sends the command to the chip?
...
-Graham
| |