From: Jose Abreu <Jose.Abreu@synopsys.com>
To: Thierry Reding <thierry.reding@gmail.com>,
Florian Fainelli <f.fainelli@gmail.com>
Cc: Jose Abreu <Jose.Abreu@synopsys.com>,
David Miller <davem@davemloft.net>,
"peppe.cavallaro@st.com" <peppe.cavallaro@st.com>,
"alexandre.torgue@st.com" <alexandre.torgue@st.com>,
"jonathanh@nvidia.com" <jonathanh@nvidia.com>,
"bbiswas@nvidia.com" <bbiswas@nvidia.com>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>
Subject: RE: [PATCH v3 0/2] net: stmmac: Enhanced addressing mode for DWMAC 4.10
Date: Thu, 26 Sep 2019 08:22:25 +0000 [thread overview]
Message-ID: <BN8PR12MB32669DDC64861CE11CA66474D3860@BN8PR12MB3266.namprd12.prod.outlook.com> (raw)
In-Reply-To: <20190925224620.GA8115@mithrandir>
From: Thierry Reding <thierry.reding@gmail.com>
Date: Sep/25/2019, 23:46:20 (UTC+00:00)
> On Wed, Sep 25, 2019 at 10:31:13AM -0700, Florian Fainelli wrote:
> > The way I would approach it (as done in bcmgenet.c) is that if the
> > platform both has CONFIG_PHYS_ADDR_T_64BIT=y and supports > 32-bits
> > addresses, then you write the upper 32-bits otherwise, you do not. Given
> > you indicate that the registers are safe to write regardless, then maybe
> > just the check on CONFIG_PHYS_ADDR_T_64BIT is enough for your case. The
> > rationale in my case is that register writes to on-chip descriptors are
> > fairly expensive (~200ns per operation) and get in the hot-path.
> >
> > The CONFIG_PHYS_ADDR_T_64BIT check addresses both native 64-bit
> > platforms (e.g.: ARM64) and those that do support LPAE (ARM LPAE for
> > instance).
>
> I think we actually want CONFIG_DMA_ADDR_T_64BIT here because we're
> dealing with addresses returned from the DMA API here.
>
> I can add an additional condition for the upper 32-bit register writes,
> something like:
>
> if (IS_ENABLED(CONFIG_DMA_ADDR_T_64BIT) && priv->dma_cfg->eame)
> ...
>
> The compiler should be able to eliminate that as dead code on platforms
> that don't support 64-bit DMA addresses, but the code should still be
> compiler regardless of the setting, thus increasing the compile
> coverage.
I'm fine with this. Some notes:
a) Do not try to enable dma_cfg->eame if CONFIG_DMA_ADDR_T_64BIT is not
enabled;
b) You can even add a likely() around priv->dma_cfg->eame check because
if a given SoC supports 64 bit addressing then its highly probable that
the IP will also support EAME.
---
Thanks,
Jose Miguel Abreu
next prev parent reply other threads:[~2019-09-26 8:22 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-20 17:00 [PATCH v3 0/2] net: stmmac: Enhanced addressing mode for DWMAC 4.10 Thierry Reding
2019-09-20 17:00 ` [PATCH v3 1/2] net: stmmac: Only enable enhanced addressing mode when needed Thierry Reding
2019-09-20 17:00 ` [PATCH v3 2/2] net: stmmac: Support enhanced addressing mode for DWMAC 4.10 Thierry Reding
2019-09-20 17:02 ` [PATCH v3 0/2] net: stmmac: Enhanced " Florian Fainelli
2019-09-21 1:35 ` Thierry Reding
2019-09-24 19:45 ` David Miller
2019-09-25 10:44 ` Jose Abreu
2019-09-25 11:33 ` David Miller
2019-09-25 11:41 ` Jose Abreu
2019-09-25 11:46 ` Jose Abreu
2019-09-25 17:31 ` Florian Fainelli
2019-09-25 22:46 ` Thierry Reding
2019-09-26 8:22 ` Jose Abreu [this message]
2019-09-25 12:01 ` David Miller
2019-09-25 11:17 ` Thierry Reding
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