linux-kernel - Re: [PATCH 1/2] spi: cadence-quadspi: Disable Auto-HW polling

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Date:   Wed, 14 Jul 2021 17:28:05 +0100
From:   Mark Brown <broonie@...nel.org>
To:     "Nandan, Apurva" <a-nandan@...com>
Cc:     linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Pratyush Yadav <p.yadav@...com>,
        Vignesh Raghavendra <vigneshr@...com>
Subject: Re: [PATCH 1/2] spi: cadence-quadspi: Disable Auto-HW polling

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?

> 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.

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