From mboxrd@z Thu Jan 1 00:00:00 1970 From: davem@davemloft.net (David Miller) Date: Tue, 04 Nov 2014 11:28:58 -0500 (EST) Subject: net: fec: fix regression on i.MX28 introduced by rx_copybreak support In-Reply-To: <20141104112912.2be8bf1a@ipc1.ka-ro> References: <20141030.121710.1524000348187962764.davem@davemloft.net> <20141031063210.69004315@ipc1.ka-ro> <20141104112912.2be8bf1a@ipc1.ka-ro> Message-ID: <20141104.112858.356827532569349127.davem@davemloft.net> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org From: Lothar Wa?mann Date: Tue, 4 Nov 2014 11:29:12 +0100 > Hi David, > > Lothar Wa?mann wrote: >> David Miller wrote: >> > From: Lothar Wa?mann >> > Date: Thu, 30 Oct 2014 07:51:04 +0100 >> > >> > >> Also, I don't thnk your DIV_ROUND_UP() eliminate for the loop >> > >> in swap_buffer() is valid. The whole point is that the current >> > >> code handles buffers which have a length which is not a multiple >> > >> of 4 properly, after your change it will no longer do so. >> > >> >> > > Do you really think so? >> > >> > Yes, because you're rounding down so you'll miss the final >> > partial word (if any). >> > >> Nope. DIV_ROUND_UP() would give '1' as upper bound for lengths from 1 to >> 4, '2' for lengths from 5 to 8 and so on. >> >> The loop with increment 4 and i < len does exactly the same. >> Try it for yourself, if you don't believe it. >> >> > Do you still think, the loop without DIV_ROUND_UP() is incorrect, > or can this patch be applied? I haven't had the time to fully re-look into the details, I'm busy with many other things at the moment. But looking at DIV_ROUND_UP() macro it rounds up. It gives an upper bound of 4 for any value 1 to 4. Unlike what you claim. Because it goes "(n + (d - 1)) / d" Which for 'd' of 4 gives: 1 --> 4 2 --> 4 3 --> 4 4 --> 4