linux-kernel - Re: [PATCH v3 2/2] mtd: rawnand: Add NAND controller support on Intel LGM SoC

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Date:   Tue, 28 Apr 2020 16:28:26 +0800
From:   "Ramuthevar, Vadivel MuruganX" 
        <vadivel.muruganx.ramuthevar@...ux.intel.com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Boris Brezillon <boris.brezillon@...labora.com>,
        linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org,
        devicetree@...r.kernel.org, cheol.yong.kim@...el.com,
        hauke.mehrtens@...el.com, qi-ming.wu@...el.com, vigneshr@...com,
        arnd@...db.de, richard@....at, brendanhiggins@...gle.com,
        linux-mips@...r.kernel.org, robh+dt@...nel.org, tglx@...utronix.de,
        masonccyang@...c.com.tw, andriy.shevchenko@...el.com
Subject: Re: [PATCH v3 2/2] mtd: rawnand: Add NAND controller support on Intel
 LGM SoC

Hi Miquel,

On 28/4/2020 3:54 pm, Miquel Raynal wrote:
> Hello,
> 
> "Ramuthevar, Vadivel MuruganX"
> <vadivel.muruganx.ramuthevar@...ux.intel.com> wrote on Tue, 28 Apr 2020
> 15:50:06 +0800:
> 
>> Hi Miquel,
>>
>> On 28/4/2020 3:40 pm, Miquel Raynal wrote:
>>> Hi Vadivel MuruganX,
>>>
>>> "Ramuthevar, Vadivel MuruganX"
>>> <vadivel.muruganx.ramuthevar@...ux.intel.com> wrote on Tue, 28 Apr 2020
>>> 14:50:35 +0800:
>>>    
>>>> Hi Boris,
>>>>
>>>> On 28/4/2020 2:47 pm, Boris Brezillon wrote:
>>>>> On Tue, 28 Apr 2020 14:40:58 +0800
>>>>> "Ramuthevar, Vadivel MuruganX"
>>>>> <vadivel.muruganx.ramuthevar@...ux.intel.com> wrote:
>>>>>     >>>> Hi Boris,
>>>>>>
>>>>>> On 28/4/2020 2:27 pm, Boris Brezillon wrote:
>>>>>>> On Tue, 28 Apr 2020 14:17:30 +0800
>>>>>>> "Ramuthevar, Vadivel MuruganX"
>>>>>>> <vadivel.muruganx.ramuthevar@...ux.intel.com> wrote:
>>>>>>>      >>>> Hi Miquel,
>>>>>>>>
>>>>>>>>         Thank you very much for the review comments and your time...
>>>>>>>>
>>>>>>>> On 27/4/2020 11:51 pm, Miquel Raynal wrote:
>>>>>>>>> Hi Ramuthevar,
>>>>>>>>>         >>>>>>> +static int ebu_nand_probe(struct platform_device *pdev)
>>>>>>>>>>> +{
>>>>>>>>>>> +	struct device *dev = &pdev->dev;
>>>>>>>>>>> +	struct ebu_nand_controller *ebu_host;
>>>>>>>>>>> +	struct nand_chip *nand;
>>>>>>>>>>> +	phys_addr_t nandaddr_pa;
>>>>>>>>>>> +	struct mtd_info *mtd;
>>>>>>>>>>> +	struct resource *res;
>>>>>>>>>>> +	int ret;
>>>>>>>>>>> +	u32 cs;
>>>>>>>>>>> +
>>>>>>>>>>> +	ebu_host = devm_kzalloc(dev, sizeof(*ebu_host), GFP_KERNEL);
>>>>>>>>>>> +	if (!ebu_host)
>>>>>>>>>>> +		return -ENOMEM;
>>>>>>>>>>> +
>>>>>>>>>>> +	ebu_host->dev = dev;
>>>>>>>>>>> +	nand_controller_init(&ebu_host->controller);
>>>>>>>>>>> +
>>>>>>>>>>> +	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "ebunand");
>>>>>>>>>>> +	ebu_host->ebu_addr = devm_ioremap_resource(&pdev->dev, res);
>>>>>>>>>>> +	if (IS_ERR(ebu_host->ebu_addr))
>>>>>>>>>>> +		return PTR_ERR(ebu_host->ebu_addr);
>>>>>>>>>>> +
>>>>>>>>>>> +	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "hsnand");
>>>>>>>>>>> +	ebu_host->nand_addr = devm_ioremap_resource(&pdev->dev, res);
>>>>>>>>>>> +	if (IS_ERR(ebu_host->nand_addr))
>>>>>>>>>>> +		return PTR_ERR(ebu_host->nand_addr);
>>>>>>>>>>> +
>>>>>>>>>>> +	ret = device_property_read_u32(dev, "nand,cs", &cs);
>>>>>>>>>>
>>>>>>>>>> CS ids should be encoded in the reg property (see [1]).
>>>>>>>>>
>>>>>>>>> Is it your choice to only support a single CS or is it actually a
>>>>>>>>> controller limitation?
>>>>>>>>
>>>>>>>> Yes , its controller limitation to support only one CS
>>>>>>>
>>>>>>> I'm pretty sure that's not true, otherwise you wouldn't have to select
>>>>>>> the CS you want to use :P.
>>>>>>
>>>>>> At a time it supports only one chip select.
>>>>>
>>>>> Yes, like 99% of the NAND controllers, but that doesn't mean you can't
>>>>> support multi-CS chips. All you have to do is attach an array of
>>>>> ebu_nand_cs to your ebu_nand_chip (as done in the atmel driver I
>>>>> pointed to). nand_operation.cs tells you which CS (index in your
>>>>> ebu_nand_cs array) a specific operation is targeting, and you can pick
>>>>> the right MMIO range/reg value based on that.
>>>>
>>>> Agreed, sure I will add that and update next series of patches .
>>>
>>> There are also many other places where you assume blindly that there
>>> is only one CS. You can check the Atmel NAND controller driver as Boris
>>> said and we will probably propose more little changes to be more
>>> generic.
>> since LGM EBU_NAND controller supports only one chip select at a time, so assumed like that, will change as generic way if consider like more chip select supports, Thanks!
> 
> What do you mean "at a time"?

I mean it supports multi-CS, during the run time it selects one.
Thanks!

Regards
Vadivel
> 
> Do we have access to the spec or a register map? We could tell you very
> quickly if it is worth the trouble. But I am pretty sure as well that
> the controller supports more than 1 CS.
> 
>> Sure , I will do the changes as per your review comments.
>>>
>>> Thanks,
>>> Miquèl
>>>    
> 
> Thanks,
> Miquèl
>