linux-kernel - Re: [PATCH v2 2/6] memory: ti-aemif: Export aemif_set_cs

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Message-ID: <07cd5d53-ce99-4ada-a7f1-53795eff5c42@bootlin.com>
Date: Tue, 12 Nov 2024 10:13:38 +0100
From: Bastien Curutchet <bastien.curutchet@...tlin.com>
To: Miquel Raynal <miquel.raynal@...tlin.com>
Cc: Santosh Shilimkar <ssantosh@...nel.org>,
 Krzysztof Kozlowski <krzk@...nel.org>, Richard Weinberger <richard@....at>,
 Vignesh Raghavendra <vigneshr@...com>, linux-kernel@...r.kernel.org,
 linux-mtd@...ts.infradead.org,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 Herve Codina <herve.codina@...tlin.com>,
 Christopher Cordahi <christophercordahi@...ometrics.ca>
Subject: Re: [PATCH v2 2/6] memory: ti-aemif: Export aemif_set_cs_timings()

Hi Miquèl,

On 11/11/24 8:21 PM, Miquel Raynal wrote:
> 
> Hello Bastien,
> 
> On 06/11/2024 at 09:55:03 +01, Bastien Curutchet <bastien.curutchet@...tlin.com> wrote:
> 
>> Export the aemif_set_cs_timing() symbol so it can be used by other
>> drivers
>>
>> Add a spinlock to protect the CS configuration register from concurrent
>> accesses.
> 
> What concurrent accesses are you trying to protect yourself against?
> I fail to see the use case, but TBH I haven't tried hard enough maybe.
> 

The register that handles the CS configuration belongs to the AEMIF 
component but it will also be accessed by the AEMIF 'children' with the 
aemif_set_cs_timing() function. So far, concurrent accesses shouldn't 
occur because the AEMIF configures the CS timings only once and does so 
before probing its 'children'; but I don't know how things can evolve in 
the future.

> Also, what justifies the use of a spin-lock in this case?
> 

TBH, I always struggle to choose between mutexes and spin-locks. I chose 
spin-lock because it only protects one memory-mapped register so I think 
it doesn't worth going to sleep when waiting for the lock.

Best regards,
Bastien