linux-kernel - Re: [PATCH net-next 09/16] net: mdio: Add Synopsys DW XPCS management interface support

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Message-ID: <20231205133205.3309ab91@device.home>
Date:   Tue, 5 Dec 2023 13:32:05 +0100
From:   Maxime Chevallier <maxime.chevallier@...tlin.com>
To:     Serge Semin <fancer.lancer@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        Jose Abreu <Jose.Abreu@...opsys.com>,
        Tomer Maimon <tmaimon77@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, openbmc@...ts.ozlabs.org,
        netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 09/16] net: mdio: Add Synopsys DW XPCS
 management interface support

Hi Serge,

On Tue,  5 Dec 2023 13:35:30 +0300
Serge Semin <fancer.lancer@...il.com> wrote:

> Synopsys DesignWare XPCS IP-core can be synthesized with the device CSRs
> being accessible over MCI or APB3 interface instead of the MDIO bus (see
> the CSR_INTERFACE HDL parameter). Thus all the PCS registers can be just
> memory mapped and be a subject of standard MMIO operations of course
> taking into account the way the Clause C45 CSRs mapping is defined. This
> commit is about adding a device driver for the DW XPCS Management
> Interface platform device and registering it in the framework of the
> kernel MDIO subsystem.
> 
> DW XPCS platform device is supposed to be described by the respective
> compatible string "snps,dw-xpcs-mi", CSRs memory space and optional
> peripheral bus clock source. Note depending on the INDIRECT_ACCESS DW XPCS
> IP-core synthesize parameter the memory-mapped reg-space can be
> represented as either directly or indirectly mapped Clause 45 space. In
> the former case the particular address is determined based on the MMD
> device and the registers offset (5 + 16 bits all together) within the
> device reg-space. In the later case there is only 256 lower address bits
> are utilized for the registers mapping. The upper bits are supposed to be
> written into the respective viewport CSR in order to reach the entire C45
> space.

Too bad the mdio-regmap driver can't be re-used here, it would deal
with reg width for you, for example. I guess the main reason would be
the direct vs indirect accesses ?

I do have a comment tough :

[...]

> +static inline ptrdiff_t dw_xpcs_mmio_addr_format(int dev, int reg)
> +{
> +	return FIELD_PREP(0x1f0000, dev) | FIELD_PREP(0xffff, reg);
> +}
> +
> +static inline u16 dw_xpcs_mmio_addr_page(ptrdiff_t csr)
> +{
> +	return FIELD_GET(0x1fff00, csr);
> +}
> +
> +static inline ptrdiff_t dw_xpcs_mmio_addr_offset(ptrdiff_t csr)
> +{
> +	return FIELD_GET(0xff, csr);
> +}

You shouldn't use inline in C files, only in headers.

Maxime