Modify the operation of setting qspi frequency when calling Octo controller

[rogeryou]

Summary of changes

Modify the operation of setting qspi frequency when calling Octo controller in qspi_api.c.
Because the value of hospi->Init.ClockPrescaler has been subtracted 1 in stm32l4xx_hal_ospi.c.

Impact of changes

N/A

Migration actions required

N/A

Documentation

N/A

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Pull request type

[X] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

[] No Tests required for this change (E.g docs only update)
[X] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

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Reviewers

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[ciarmcom]

@rogeryou, thank you for your changes.
@ARMmbed/mbed-os-maintainers please review.

[0xc0170]

Can you amend the commit - add there info why is this being modified, I dont understand the reasoning.

[rogeryou]

Can you amend the commit - add there info why is this being modified, I dont understand the reasoning.

div is for setting the prescaler,

If the div is 3, the value write to the controller register should be 2.
If the div is 4, the value write to the controller register should be 3.
So, we need div = div -1;
For ST QSPI controller driver , this value is set into the register directly, as the below code:

/* Configure QSPI Clock Prescaler and Sample Shift */

#if defined(QUADSPI_CR_DFM)
    MODIFY_REG(hqspi->Instance->CR, (QUADSPI_CR_PRESCALER | QUADSPI_CR_SSHIFT | QUADSPI_CR_FSEL | QUADSPI_CR_DFM),
               ((hqspi->Init.ClockPrescaler << QUADSPI_CR_PRESCALER_Pos) |
                hqspi->Init.SampleShifting  | hqspi->Init.FlashID | hqspi->Init.DualFlash));
#else
    MODIFY_REG(hqspi->Instance->CR, (QUADSPI_CR_PRESCALER | QUADSPI_CR_SSHIFT),
               ((hqspi->Init.ClockPrescaler << QUADSPI_CR_PRESCALER_Pos) |
                hqspi->Init.SampleShifting));
#endif

But for ST OSPI controller driver, before the value is set into the register , it will be subtracted 1, as the code below:
`
/* Configure clock prescaler */

     MODIFY_REG(hospi->Instance->DCR2, OCTOSPI_DCR2_PRESCALER, ((hospi->Init.ClockPrescaler - 1U) << OCTOSPI_DCR2_PRESCALER_Pos));

`

So, "div = div - 1;" should be removed.

[0xc0170]

Part of the information should be in the commit message. @ARMmbed/team-st-mcd Please review

Pull request has been modified.

[rogeryou]

Part of the information should be in the commit message. @ARMmbed/team-st-mcd Please review

Hi,
I have modify the commit message about the reason.
Is there anything else I need to do ?

[jeromecoutant]

I have modify the commit message about the reason.
Is there anything else I need to do ?

@0xc0170

[adbridge]

@0xc0170 are you ok with this now ?

[0xc0170]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 6 of 6 test jobs passed
Build number : 1
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