linux-kernel - Re: [PATCH v2 1/3] PCI: mediatek: Allocate MSI address with dmam_alloc

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Message-ID: <864ja2l2jd.wl-maz@kernel.org>
Date: Sun, 09 Jun 2024 13:32:38 +0100
From: Marc Zyngier <maz@...nel.org>
To: Manivannan Sadhasivam <mani@...nel.org>
Cc: Jianjun Wang <jianjun.wang@...iatek.com>,	Lorenzo Pieralisi
 <lpieralisi@...nel.org>,	Krzysztof Wilczyński
 <kw@...ux.com>,	Rob Herring <robh@...nel.org>,	Bjorn Helgaas
 <bhelgaas@...gle.com>,	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,	Ryder
 Lee <ryder.lee@...iatek.com>,	linux-pci@...r.kernel.org,
	linux-mediatek@...ts.infradead.org,	linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,	jieyy.yang@...iatek.com,
	chuanjia.liu@...iatek.com,	qizhong.cheng@...iatek.com,
	jian.yang@...iatek.com,	jianguo.zhang@...iatek.com
Subject: Re: [PATCH v2 1/3] PCI: mediatek: Allocate MSI address with dmam_alloc_coherent()

On Sat, 08 Jun 2024 10:01:52 +0100,
Manivannan Sadhasivam <mani@...nel.org> wrote:
> 
> On Mon, Dec 11, 2023 at 04:52:54PM +0800, Jianjun Wang wrote:
> > Use dmam_alloc_coherent() to allocate the MSI address, instead of using
> > virt_to_phys().
> > 
> 
> What is the reason for this change? So now PCIE_MSI_VECTOR becomes unused?

More importantly, this is yet another example of the DW reference
driver nonsense, where memory is allocated for *MSI*, while the whole
point of MSIs is that it is a write that doesn't target memory, making
any form of RAM allocation absolutely pointless.

This silly approach has been cargo-culted for years, and while I
caught a few in my time, you can't beat copy-paste.

IMO, this patch is only making things worse instead of fixing things.

	M.

-- 
Without deviation from the norm, progress is not possible.