Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH 1/2] spi: cadence-quadspi: Disable Auto-HW polling
To:     Mark Brown <broonie@kernel.org>
CC:     <linux-spi@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        Pratyush Yadav <p.yadav@ti.com>,
        Vignesh Raghavendra <vigneshr@ti.com>
References: <20210713125743.1540-1-a-nandan@ti.com>
 <20210713125743.1540-2-a-nandan@ti.com> <20210713182550.GG4098@sirena.org.uk>
 <f1947183-81d2-3519-d25f-71d93f59e434@ti.com>
 <20210714162805.GE4719@sirena.org.uk>
From:   Apurva Nandan <a-nandan@ti.com>
Message-ID: <dfa38823-b63f-1807-6141-682930de2f3a@ti.com>
Date:   Wed, 14 Jul 2021 23:21:59 +0530
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.11.0
MIME-Version: 1.0
In-Reply-To: <20210714162805.GE4719@sirena.org.uk>
Content-Type: text/plain; charset="windows-1252"
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk


On 14-Jul-21 9:58 PM, Mark Brown wrote:
> On Wed, Jul 14, 2021 at 06:52:12PM +0530, Nandan, Apurva wrote:
>> On 13-Jul-21 11:55 PM, Mark Brown wrote:
>>> On Tue, Jul 13, 2021 at 12:57:41PM +0000, Apurva Nandan wrote:
> 
>>>> cadence-quadspi controller doesn't allow an address phase when
>>>> auto-polling the busy bit on the status register. Unlike SPI NOR
> 
>>> Would it not be better to only disable this on NAND rather than
>>> disabling it completely?
> 
>> I am not sure how it is possible currently in the controller, could you
>> please suggest a way? Also, should we have this logic of checking flash
>> device type in the cadence-quadspi controller? SPI controller should be
>> generic to all flash cores right?
> 
> Surely the controller can tell if an address phase (or other unsupported
> feature) is present?
> 

Yeah sure, understood.

>> In my opinion, it shouldn't harm as spi-nor core doesn't depend on HW
>> polling anyways and auto-HW polling is a minor overhead.
> 
> Flash stuff seems to quite often end up happening when the system is
> heavily loaded for other reasons, it's much more of an issue with things
> that are done more with PIO but still seems useful to avoid having to
> poll in software, either it'll reduce CPU load or reduce latency and
> increase throughput.
> 

Yes, got the point. Will amend it.

Thanks,
Apurva Nandan