Re: [PATCH 00/16] mtd: spi-nor: aspeed: AST2600 support and extensions

[Cédric Le Goater <clg@xxxxxxxx>]

On 11/10/2019 11:51, Boris Brezillon wrote:
> On Fri, 11 Oct 2019 11:29:49 +0200
> Cédric Le Goater <clg@xxxxxxxx> wrote:
> 
>> On 11/10/2019 08:45, Boris Brezillon wrote:
>>> On Thu, 10 Oct 2019 23:47:45 +0000
>>> Joel Stanley <joel@xxxxxxxxx> wrote:
>>>   
>>>> On Wed, 9 Oct 2019 at 20:56, Boris Brezillon
>>>> <boris.brezillon@xxxxxxxxxxxxx> wrote:  
>>>>>
>>>>> Hi Cedric,
>>>>>
>>>>> On Fri,  4 Oct 2019 13:59:03 +0200
>>>>> Cédric Le Goater <clg@xxxxxxxx> wrote:
>>>>>    
>>>>>> Hello,
>>>>>>
>>>>>> This series first extends the support for the Aspeed AST2500 and
>>>>>> AST2400 SMC driver. It adds Dual Data support and read training giving
>>>>>> the best read settings for a given chip. Support for the new AST2600
>>>>>> SoC is added at the end.
>>>>>>
>>>>>> I understand that a new spi_mem framework exists and I do have an
>>>>>> experimental driver using it. But unfortunately, it is difficult to
>>>>>> integrate the read training. The Aspeed constraints are not compatible
>>>>>> and i haven't had the time to extend the current framework.    
>>>>>
>>>>> Hm, I don't think that's a good reason to push new features to the
>>>>> existing driver, especially since I asked others to migrate their
>>>>> drivers to spi-mem in the past. I do understand your concerns, and I'll
>>>>> let the SPI NOR/MTD maintainers make the final call, but I think it'd
>>>>> be better for the SPI MEM ecosystem to think about this link-training
>>>>> API (Vignesh needs it for the Cadence driver IIRC) rather than pushing
>>>>> this kind of feature to spi-nor controller drivers.    
>>>>
>>>> As Cedric mentioned, the OpenBMC project has been shipping the read
>>>> training code for the ast2400/ast2400 for several years now. It would
>>>> be great to see it in mainline.
>>>>
>>>> I think it's reasonable to ask for the driver to be moved to the
>>>> spi-mem subsystem once it has the required APIs.  
>>>
>>> Except it won't have the necessary APIs unless someone works on it, and
>>> adding this feature to existing spi-nor drivers won't help achieving
>>> this goal.  
>>
>>
>> What would you suggest ? Something like the patch below which would
>> call a 'train' operation at the end of spi_add_device().
> 
> This has been discussed in the past with Vignesh, but I can't find the
> thread where this discussion happened. My understanding was that link
> training would use a command with well-known output (is there a
> dedicated SPI NOR command for that?) and test different clk settings
> until it finds one that works.

The read training on Aspeed consists of finding the appropriate read
timing delays for well-known HCLK dividers and store the results in 
the Read Timing Compensation register. 

We first read a golden buffer at low speed and then perform reads with 
different clocks and delay cycle settings to find a breaking point. This 
selects the default clock frequency for the CEx control register. 

 
>> Also, when doing read training, we might need to know some lowlevel 
>> characteristics of the chip being trained. Should we offer a way 
>> to grab the probed m25p80 device and give access to the underlying 
>> 'struct spi_nor' ? 
>>
>>   static struct spi_nor *spi_get_pnor(struct spi_device *spi)
>>   {
>> 	struct spi_mem *spimem = spi_get_drvdata(spi);
>> 	struct m25p *flash = spi_mem_get_drvdata(spimem);
>>
>> 	return flash ? &flash->spi_nor : NULL;
>>   }
>>
>> Yeah, it's hideous. I just want to raise the issue.
> 
> Oh no. We definitely don't want to expose the spi_nor chip to the
> spi_mem layer, but, if needed, we can add more fields to spi_mem and
> let the spi_mem driver fill them. We just need to figure out what's
> really needed.

We need the SPI/NOR flash characteristics for link training and its 
size to configure the controller to access the CS on the AHB window. 

[ ... ]

>>  	int (*fw_translate_cs)(struct spi_controller *ctlr, unsigned cs);
>> +
>> +	int			(*train)(struct spi_device *spi);
> 
> Was more thinking of something like:
> 
> 	int (*link_setup)(struct spi_mem *mem,
> 			  struct spi_mem_op *op_template,
> 			  ...);
> 
> where the op_template would potentially differ depending on the type of
> memory (NOR, NAND, SRAM?). I also don't know what other params would be
> needed to do the link training.

The Aspeed controller needs to set read delay timings at different HCLK
settings. It's doing read operations with the default IO mode.
 
> BTW, this hook should be in the spi_mem_controller_ops struct not in
> spi_controller.

ok. Let's wait for feedback from Vinesh.

Thanks,

C. 



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