netdev - Re: [RFT][PATCH 4/7] net: dsa: microchip: Remove dev->txbuf

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Date:   Wed, 19 Dec 2018 17:20:33 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Marek Vasut <marex@...x.de>, netdev@...r.kernel.org
Cc:     andrew@...n.ch, Tristram Ha <Tristram.Ha@...rochip.com>,
        Woojung Huh <Woojung.Huh@...rochip.com>
Subject: Re: [RFT][PATCH 4/7] net: dsa: microchip: Remove dev->txbuf

On 12/19/18 5:06 PM, Marek Vasut wrote:
> Previous patches unconver that ksz_spi_write() is always ever called
> with len = 1, 2 or 4. We can thus drop the if (len > SPI_TX_BUF_LEN)
> check and we can also drop the allocation of the txbuf which is part
> of the driver data. This wastes 256 bytes for no reason and can be
> replaced with 8-byte stack allocated buffer, which is what this patch
> does. This is an intermediate step though, which will go away after
> regmap conversion.

dev is a kmalloc'd buffer, so dev->txbuf is a DMA-able buffer, that
could be presumably why it was used in the first place, DMA from the
stack is not something safe, but I did not check the core SPI layer or
the SPI bus master driver to see whether they do take care of that already.
-- 
Florian