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 08:47:04 +0200
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     "Ramuthevar, Vadivel MuruganX" 
        <vadivel.muruganx.ramuthevar@...ux.intel.com>
Cc:     Miquel Raynal <miquel.raynal@...tlin.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

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.