linux-kernel - Re: [PATCH v3 01/13] PCI: imx6: Simplify clock handling by using HAS_CLK

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Message-ID: <20231212225426.GB2948988-robh@kernel.org>
Date:   Tue, 12 Dec 2023 16:54:26 -0600
From:   Rob Herring <robh@...nel.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     Frank Li <Frank.Li@....com>, bhelgaas@...gle.com,
        conor+dt@...nel.org, devicetree@...r.kernel.org,
        festevam@...il.com, helgaas@...nel.org, hongxing.zhu@....com,
        imx@...ts.linux.dev, kernel@...gutronix.de,
        krzysztof.kozlowski+dt@...aro.org, kw@...ux.com,
        l.stach@...gutronix.de, linux-arm-kernel@...ts.infradead.org,
        linux-imx@....com, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, lpieralisi@...nel.org,
        s.hauer@...gutronix.de, shawnguo@...nel.org
Subject: Re: [PATCH v3 01/13] PCI: imx6: Simplify clock handling by using
 HAS_CLK_* bitmask

On Tue, Dec 12, 2023 at 10:19:13PM +0530, Manivannan Sadhasivam wrote:
> On Mon, Dec 11, 2023 at 04:58:30PM -0500, Frank Li wrote:
> > Refactors the clock handling logic in the imx6 PCI driver by adding
> > HAS_CLK_* bitmask define for drvdata::flags . Simplifies the code and makes
> > it more maintainable, as future additions of SOC support will only require
> > straightforward changes. The drvdata::flags and a bitmask ensures a cleaner
> > and more scalable switch-case structure for handling clocks.
> > 
> 
> Is there any necessity to validate each clock in the driver? I mean, can't you
> just rely on devicetree to provide enough clocks for the functioning of the PCIe
> controller?
> 
> If you can rely on devicetree (everyone should in an ideal world), then you can
> just use devm_clk_bulk_get_all() to get all available clocks for the SoC and
> just enable/disable whatever is available.

Or just use the *_get_optional() variants of functions. They return NULL 
such that subsequent calls are just NOPs if the resource is not present. 
Of course, they aren't really optional on any given platform in this 
case, but does that really matter.

There isn't an optional variant for phys, but it can be added.

> 
> This will greatly simplify the code.
> 
> Only downside of this approach is, if the devicetree is not supplying enough
> clocks, then it will be difficult to find why PCIe is not working. But this also
> means that the devicetree is screwed.

A sufficient schema should prevent that... That's what they're for, not 
just torturing people to learn json-schema. :)

Rob