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Date:   Thu, 4 Feb 2021 10:31:52 +0100
From:   Miquel Raynal <miquel.raynal@bootlin.com>
To:     Boris Brezillon <boris.brezillon@collabora.com>
Cc:     Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>,
        richard@nod.at, vigneshr@ti.com, linux-mtd@lists.infradead.org,
        linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        bjorn.andersson@linaro.org
Subject: Re: [PATCH] mtd: rawnand: Do not check for bad block if bbt is
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Hi Boris,

Boris Brezillon <boris.brezillon@collabora.com> wrote on Thu, 4 Feb
2021 10:27:38 +0100:

> On Thu, 4 Feb 2021 10:04:08 +0100
> Miquel Raynal <miquel.raynal@bootlin.com> wrote:
> 
> > Hi Boris,
> > 
> > Boris Brezillon <boris.brezillon@collabora.com> wrote on Thu, 4 Feb
> > 2021 09:59:45 +0100:
> >   
> > > On Thu, 4 Feb 2021 14:22:21 +0530
> > > Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> wrote:
> > >     
> > > > On Thu, Feb 04, 2021 at 09:13:36AM +0100, Miquel Raynal wrote:      
> > > > > Hi Manivannan,
> > > > > 
> > > > > Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> wrote on Wed,
> > > > > 03 Feb 2021 17:11:31 +0530:
> > > > >         
> > > > > > On 3 February 2021 4:54:22 PM IST, Boris Brezillon <boris.brezillon@collabora.com> wrote:        
> > > > > > >On Wed, 03 Feb 2021 16:22:42 +0530
> > > > > > >Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> wrote:
> > > > > > >          
> > > > > > >> On 3 February 2021 3:49:14 PM IST, Boris Brezillon          
> > > > > > ><boris.brezillon@collabora.com> wrote:          
> > > > > > >> >On Wed, 03 Feb 2021 15:42:02 +0530
> > > > > > >> >Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> wrote:
> > > > > > >> >            
> > > > > > >> >> >> 
> > > > > > >> >> >> I got more information from the vendor, Telit. The access to          
> > > > > > >the            
> > > > > > >> >3rd              
> > > > > > >> >> >partition is protected by Trustzone and any access in non          
> > > > > > >privileged          
> > > > > > >> >> >mode (where Linux kernel runs) causes kernel panic and the device
> > > > > > >> >> >reboots.             
> > > > > > >> >
> > > > > > >> >Out of curiosity, is it a per-CS-line thing or is this section
> > > > > > >> >protected on all CS?
> > > > > > >> >            
> > > > > > >> 
> > > > > > >> Sorry, I didn't get your question.           
> > > > > > >
> > > > > > >The qcom controller can handle several chips, each connected through a
> > > > > > >different CS (chip-select) line, right? I'm wondering if the firmware
> > > > > > >running in secure mode has the ability to block access for a specific
> > > > > > >CS line or if all CS lines have the same constraint. That will impact
> > > > > > >the way you describe it in your DT (in one case the secure-region
> > > > > > >property should be under the controller node, in the other case it
> > > > > > >should be under the NAND chip node).          
> > > > > > 
> > > > > > Right. I believe the implementation is common to all NAND chips so the property should be in the controller node.         
> > > > > 
> > > > > Looks weird: do you mean that each of the chips will have a secure area?        
> > > > 
> > > > I way I said is, the "secure-region" property will be present in the controller
> > > > node and not in the NAND chip node since this is not related to the device
> > > > functionality.
> > > > 
> > > > But for referencing the NAND device, the property can have the phandle as below:
> > > > 
> > > > secure-region = <&nand0 0xffff>;      
> > > 
> > > My question was really what happens from a functional PoV. If you have
> > > per-chip protection at the FW level, this property should be under the
> > > NAND node. OTH, if the FW doesn't look at the selected chip before
> > > blocking the access, it should be at the controller level. So, you
> > > really have to understand what the secure FW does.    
> > 
> > I'm not so sure actually, that's why I like the phandle to nand0 -> in
> > any case it's not a property of the NAND chip itself, it's kind of a
> > host constraint, so I don't get why the property should be at the
> > NAND node level?  
> 
> I would argue that we already have plenty of NAND properties that
> encode things controlled by the host (ECC, partitions, HW randomizer,
> boot device, and all kind of controller specific stuff) :P. Having
> the props under the NAND node makes it clear what those things are
> applied to, and it's also easier to parse for the driver (you already
> have to parse each node to get the reg property anyway).

Fair points.

> > Also, we should probably support several secure regions (which could be
> > a way to express the fact that the FW does not look at the CS)?  
> 
> Sure, the secure-region should probably be renamed secure-regions, even
> if it's defined at the NAND chip level.

Absolutely.

Thanks,
Miquèl