Re: [PATCH 2/2] mtd: spi-nor: add driver for STM32 quad spi flash controller

On 03/29/2017 06:38 PM, Ludovic BARRE wrote:

On 03/29/2017 03:57 PM, Marek Vasut wrote:

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On 03/29/2017 03:35 PM, Ludovic BARRE wrote:

[...]

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+    writel_relaxed(CR_PRESC(presc) | CR_FTHRES(3) | CR_TCEN |
CR_SSHIFT
+               | CR_EN, qspi->io_base + QUADSPI_CR);
+
+    /* a minimum fsize must be set to sent the command id */
+    flash->fsize = 25;

I don't understand why this is needed and the comment doesn't make
sense. Please fix.

fsize field defines the size of external memory.

What external memory ? Unclear

oops, fsize field defined the size of "flash memory" in stm32 qspi
controller.

Errr, now I am totally lost :) Is that some internal SPI NOR ? Shouldn't
the size be coming from DT or something ?

quoted

Number of bytes in Flash memory = 2 ^[FSIZE+1].
To sent a nor cmd this field must be set (hardware issue),
but before "spi_nor_scan" the size of flash nor is not know.
So I set a temporary value (workaround).

Is it needed before the scan ?

yes it's needed before scan (fix a "stm32 qspi controller" issue)

sorry, I try to reformulate:

The nor flash (external component like micron n25q128a13
or spansion s25fl512s ...) is connected to stm32 by classic
spi-nor interface cs, clock and 1/2/4 IO lines.

the stm32 microprocessor has a dedicated controller to
manage spi-nor interface, it's stm32 qspi.

In stm32 qspi controller there is a register with fsize field
which define the size of nor flash (n25q128a13 or s25fl512s...).

fsize can't be null, else the stm32 qspi controller doesn't send
spi-nor command. it's "stm32 qspi controller" issue.

Before the "spi_nor_scan" the size of nor flash (n25q128a13
or s25fl512s...) is not know. So we set a temporary value just
to discover the nor flash with "spi_nor_scan". After we can
set the right value (mtd->size) in fsize.

I see, now it makes sense. Such a beefy comment would be nice :)

-- 
Best regards,
Marek Vasut

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