[RFC PATCH 4/6] spi: ti-qspi: Implement the spi_mem interface

[Schrempf Frieder]

Hi Boris, hi Vignesh,

On 14.02.2018 20:09, Boris Brezillon wrote:
> On Wed, 14 Feb 2018 21:55:10 +0530
> Vignesh R <vigneshr at ti.com> wrote:
> 
>> On 12-Feb-18 9:38 PM, Boris Brezillon wrote:
>>> On Mon, 12 Feb 2018 21:30:09 +0530
>>> Vignesh R <vigneshr at ti.com> wrote:
>>>    
>>>> On 12-Feb-18 6:01 PM, Boris Brezillon wrote:
>>>>> On Mon, 12 Feb 2018 17:13:55 +0530
>>>>> Vignesh R <vigneshr at ti.com> wrote:
>>>>>      
>>>>>> On Tuesday 06 February 2018 04:51 AM, Boris Brezillon wrote:
>>>>>>> From: Boris Brezillon <boris.brezillon at free-electrons.com>
>>>>>>>
>>>>>>> The spi_mem interface is meant to replace the spi_flash_read() one.
>>>>>>> Implement the ->exec_op() method so that we can smoothly get rid of the
>>>>>>> old interface.
>>>>>>>
>>>>>>> Signed-off-by: Boris Brezillon <boris.brezillon at free-electrons.com>
>>>>>>> ---
>>>>>>>    drivers/spi/spi-ti-qspi.c | 85 +++++++++++++++++++++++++++++++++++++++--------
>>>>>>>    1 file changed, 72 insertions(+), 13 deletions(-)
>>>>>>>
>>>>>>> diff --git a/drivers/spi/spi-ti-qspi.c b/drivers/spi/spi-ti-qspi.c
>>>>>>> index c24d9b45a27c..40cac3ef6cc9 100644
>>>>>>> --- a/drivers/spi/spi-ti-qspi.c
>>>>>>> +++ b/drivers/spi/spi-ti-qspi.c
>>>>>>
>>>>>> [...]
>>>>>>      
>>>>>>> +static const struct spi_controller_mem_ops ti_qspi_mem_ops = {
>>>>>>> +   .exec_op = ti_qspi_exec_mem_op,
>>>>>>
>>>>>>          .supports_op = ti_qspi_supports_mem_op,
>>>>>>
>>>>>> Its required as per spi_controller_check_ops() in Patch 1/6
>>>>>      
>>>>> ->supports_op() is optional, and if it's missing, the core will do the
>>>>> regular QuadSPI/DualSPI/SingleSPI check (see spi_mem_supports_op()
>>>>> implementation).
>>>>
>>>> You might have overlooked spi_controller_check_ops() from Patch 1/6:
>>>> +static int spi_controller_check_ops(struct spi_controller *ctlr)
>>>> +{
>>>> +	/*
>>>> +	 * The controller can implement only the high-level SPI-memory
>>>> +	 * operations if it does not support regular SPI transfers.
>>>> +	 */
>>>> +	if (ctlr->mem_ops) {
>>>> +		if (!ctlr->mem_ops->supports_op ||
>>>> +		    !ctlr->mem_ops->exec_op)
>>>> +			return -EINVAL;
>>>> +	} else if (!ctlr->transfer && !ctlr->transfer_one &&
>>>> +		   !ctlr->transfer_one_message) {
>>>> +		return -EINVAL;
>>>> +	}
>>>> +
>>>> +	return 0;
>>>> +}
>>>> +
>>>>
>>>> So if ->supports_op() is not populated by SPI controller driver, then
>>>> driver probe fails with -EINVAL. This is what I observed on my TI
>>>> hardware when testing this patch series.
>>>
>>> Correct. Then I should fix spi_controller_check_ops() to allow empty
>>> ctlr->mem_ops->supports_op.
>>>    
>>>>   
>>>>> This being said, if you think a custom ->supports_op()
>>>>> implementation is needed for this controller I can add one.
>>>>>      
>>>>
>>>> spi_mem_supports_op() should suffice for now if above issue is fixed.
>>>
>>> Cool. IIUC, you tested the series on a TI SoC. Does it work as
>>> expected? Do you see any perf regressions?
>>>    
>>
>> I am planning to collect throughput numbers with this series for TI
>> QSPI. I don't think there would be noticeable degradation.
> 
> Ok.
> 
>> But, it would be interesting to test for a driver thats now under
>> drivers/mtd/spi-nor moved to drivers/spi and see if added overhead of
>> m25p80 layer + spi core has any impact.
> 
> I'm working with Frieder on the fsl-qspi rework, so we should have
> numbers soon.

I made a speed comparison between fsl-quadspi.c and Boris' 
spi-fsl-qspi.c using a Micron MT25QL512 64MB NOR: [1]

It seems like the spi-mem-based driver is slower up to about 40%.

I had to remove USE_FSR, as FSR read/write doesn't work with both drivers:

-       { "n25q512ax3",  INFO(0x20ba20, 0, 64 * 1024, 1024, SECT_4K | 
USE_FSR | SPI_NOR_QUAD_READ) },
+       { "n25q512ax3",  INFO(0x20ba20, 0, 64 * 1024, 1024, SECT_4K | 
SPI_NOR_QUAD_READ) },

For the spi-mem driver I set spi-tx-bus-width = <1> to match with 
fsl-quadspi.c (does not use quad write).
My dts looks like this for both cases:

&qspi {
     pinctrl-names = "default";
     pinctrl-0 = <&pinctrl_qspi>;
     status = "okay";

     flash0: n25q512ax3 at 0 {
         #address-cells = <1>;
         #size-cells = <1>;
         compatible = "micron,n25q512ax3", "jedec,spi-nor";
         spi-max-frequency = <108000000>;
         spi-rx-bus-width = <4>;
         spi-tx-bus-width = <1>;
         reg = <0>;
     };
};

Regards,

Frieder

[1]: https://paste.ee/p/dc9KM