linux-kernel - Re: [PATCH v2 RFC net-next 03/18] net: mvpp2: add CM3 SRAM memory map

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Date:   Sun, 24 Jan 2021 19:51:13 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     stefanc@...vell.com, netdev@...r.kernel.org,
        thomas.petazzoni@...tlin.com, davem@...emloft.net,
        nadavh@...vell.com, ymarkman@...vell.com,
        linux-kernel@...r.kernel.org, kuba@...nel.org, mw@...ihalf.com,
        atenart@...nel.org
Subject: Re: [PATCH v2 RFC net-next 03/18] net: mvpp2: add CM3 SRAM memory map

On Sun, Jan 24, 2021 at 12:44:43PM +0000, Russell King - ARM Linux admin wrote:
> On Sun, Jan 24, 2021 at 01:43:52PM +0200, stefanc@...vell.com wrote:
> > +		priv->sram_pool = of_gen_pool_get(dn, "cm3-mem", 0);
> > +		if (!priv->sram_pool) {
> > +			if (!defer_once) {
> > +				defer_once = true;
> > +				/* Try defer once */
> > +				return -EPROBE_DEFER;
> > +			}
> > +			dev_warn(&pdev->dev, "DT is too old, Flow control not supported\n");
> > +			return -ENOMEM;
> > +		}
> > +		priv->cm3_base = (void __iomem *)gen_pool_alloc(priv->sram_pool,
> > +								MSS_SRAM_SIZE);
> > +		if (!priv->cm3_base)
> > +			return -ENOMEM;
> 
> This probably could do with a comment indicating that it is reliant on
> this allocation happening at offset zero into the SRAM. The only reason
> that is guaranteed _at the moment_ is because the SRAM mapping is 0x800
> bytes in size, and you are requesting 0x800 bytes in this allocation,
> so allocating the full size.

Hi Russell

I'm wondering if using a pool even makes sense. The ACPI case just
ioremap() the memory region. Either this memory is dedicated, and then
there is no need to use a pool, or the memory is shared, and at some
point the ACPI code is going to run into problems when some other
driver also wants access.

       Andrew