Re: [PATCH v4 2/2] mtd: rawnand: Add NAND controller support on Intel LGM SoC

From: Boris Brezillon <boris.brezillon@collabora.com>
To: "Ramuthevar,
	Vadivel MuruganX"  <vadivel.muruganx.ramuthevar@linux.intel.com>,
	qi-ming.wu@intel.com
Cc: linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org,
	devicetree@vger.kernel.org, cheol.yong.kim@intel.com,
	hauke.mehrtens@intel.com, anders.roxell@linaro.org,
	vigneshr@ti.com, arnd@arndb.de, richard@nod.at,
	brendanhiggins@google.com, linux-mips@vger.kernel.org,
	robh+dt@kernel.org, miquel.raynal@bootlin.com,
	tglx@linutronix.de, masonccyang@mxic.com.tw,
	andriy.shevchenko@intel.com
Subject: Re: [PATCH v4 2/2] mtd: rawnand: Add NAND controller support on Intel LGM SoC
Date: Wed, 29 Apr 2020 16:48:32 +0200	[thread overview]
Message-ID: <20200429164832.6800fc70@collabora.com> (raw)
In-Reply-To: <9d77c64c-d0f9-7a13-3391-d05bf458bdb1@linux.intel.com>

On Wed, 29 Apr 2020 22:33:37 +0800
"Ramuthevar, Vadivel MuruganX"
<vadivel.muruganx.ramuthevar@linux.intel.com> wrote:

> Hi Boris,
> 
> On 29/4/2020 10:22 pm, Boris Brezillon wrote:
> > On Wed, 29 Apr 2020 18:42:05 +0800
> > "Ramuthevar, Vadivel MuruganX"
> > <vadivel.muruganx.ramuthevar@linux.intel.com> wrote:
> >   
> >> +
> >> +#define EBU_ADDR_SEL(n)		(0x20 + (n) * 4)
> >> +#define EBU_ADDR_MASK		(5 << 4)  
> > 
> > It's still unclear what ADDR_MASK is for. Can you add a comment
> > explaining what it does?  
> 
> Thank you Boris, keep review and giving inputs, will update.

Can you please explain it here before sending a new version?

> >   
> >> +#define EBU_ADDR_SEL_REGEN	0x1  
> > 
> >   
> >> +
> >> +	writel(lower_32_bits(ebu_host->cs[ebu_host->cs_num].nand_pa) |
> >> +	       EBU_ADDR_SEL_REGEN | EBU_ADDR_MASK,
> >> +	       ebu_host->ebu + EBU_ADDR_SEL(reg));
> >> +
> >> +	writel(EBU_MEM_BASE_CS_0 | EBU_ADDR_MASK | EBU_ADDR_SEL_REGEN,
> >> +	       ebu_host->ebu + EBU_ADDR_SEL(0));
> >> +	writel(EBU_MEM_BASE_CS_1 | EBU_ADDR_MASK | EBU_ADDR_SEL_REGEN,
> >> +	       ebu_host->ebu + EBU_ADDR_SEL(reg));  
> > 
> > That's super weird. You seem to set EBU_ADDR_SEL(reg) twice. Are you
> > sure that's needed, and are we setting EBU_ADDR_SEL(0) here?  
> 
> You are right, its weird only, but we need it, since different chip 
> select has different memory region access address.

Well, that doesn't make any sense, the second write to
EBU_ADDR_SEL(reg) overrides the first one, meaning that nand_pa is
actually never written to ADDR_SEL(reg).

> 
> Yes , we are setting both CS0 and CS1 memory access region, if you have 
> any concern to optimize, please suggest me, Thanks!

If you want to setup both CS, and the address written in EBU_ADDR_SEL(x)
is really related to the nand_pa address, then retrieve resources for
all CS ranges. If it's not related, please explain what those
EBU_MEM_BASE_CS_X values encode.