From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tomasz Figa Subject: Re: [RFC PATCH 06/11] dma: amba-pl08x: Keep LLIs aligned to 4-word boundary Date: Mon, 17 Jun 2013 11:28:57 -0700 (PDT) Message-ID: <1689769.rtxlYhhpTQ@flatron> References: <1371416058-22047-1-git-send-email-tomasz.figa@gmail.com> <1371416058-22047-7-git-send-email-tomasz.figa@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Linus Walleij Cc: "alsa-devel@alsa-project.org" , Heiko =?ISO-8859-1?Q?St=FCbner?= , Padmavathi Venna , Takashi Iwai , Alessandro Rubini , "linux-kernel@vger.kernel.org" , Giancarlo Asnaghi , Kukjin Kim , Russell King - ARM Linux , Vinod Koul , Thomas Abraham , Grant Likely , Arnd Bergmann , linux-samsung-soc , Sylwester Nawrocki , Jaroslav Kysela , "linux-arm-kernel@lists.infradead.org" , Sangbeom Kim , Liam Girdwood , linux-spi@vger.kernel. List-Id: alsa-devel@alsa-project.org On Monday 17 of June 2013 15:51:20 Linus Walleij wrote: > On Sun, Jun 16, 2013 at 10:54 PM, Tomasz Figa wrote: > > PL080 reference manual states that to LLI entries should be aligned > > to 4-word boundary to make LLI fetches more efficient. This patch adds > > a 3-word padding to the LLi struct to make this condition true. > > > > Signed-off-by: Tomasz Figa > > --- > > > > drivers/dma/amba-pl08x.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/drivers/dma/amba-pl08x.c b/drivers/dma/amba-pl08x.c > > index eb10eb8..0da5539 100644 > > --- a/drivers/dma/amba-pl08x.c > > +++ b/drivers/dma/amba-pl08x.c > > @@ -127,6 +127,7 @@ struct pl08x_lli { > > > > u32 lli; > > u32 cctl; > > u32 cctl1; > > > > + u32 dummy[3]; > > Atleast put a comment into the code explaining what this is all > about. Or someone will add another member to the struct and > all is lost. Call it "padding" rather than dummy. > > > }; > > So it used to be like this before you added cctl1: > > struct pl08x_lli { > u32 src; > u32 dst; > u32 lli; > u32 cctl; > }; > > Meaning it was 3 words. > > And now you make it take 8 words for everyone. > > Atleast this patch should be squashed into the patch > adding cctl1. > > But I really don't like this fragile way of casting structs right > into memory, and I don't like that teh other PL080's also have > to waste 8 words when their LLIs fit so nicely into 4. > > I would have solved this problem by creating a > marshalling function that just allocate the number of bytes the > LLI entry shall have and fill it in by assigning directly to the > precise target memory cell. This way the LLIs will take > 4 words on the original variants and you can use some > nice logic to pad out to 8 words on the PL080S variant. Definitely a valid point. I'll see what I can do about it. I was thinking about it originally, but I couldn't find any really good solution for this so I just went with this extremely simple approach as a proof of concept and to show the problem. :) Best regards, Tomasz From mboxrd@z Thu Jan 1 00:00:00 1970 From: tomasz.figa@gmail.com (Tomasz Figa) Date: Mon, 17 Jun 2013 11:28:57 -0700 (PDT) Subject: [RFC PATCH 06/11] dma: amba-pl08x: Keep LLIs aligned to 4-word boundary In-Reply-To: References: <1371416058-22047-1-git-send-email-tomasz.figa@gmail.com> <1371416058-22047-7-git-send-email-tomasz.figa@gmail.com> Message-ID: <1689769.rtxlYhhpTQ@flatron> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Monday 17 of June 2013 15:51:20 Linus Walleij wrote: > On Sun, Jun 16, 2013 at 10:54 PM, Tomasz Figa wrote: > > PL080 reference manual states that to LLI entries should be aligned > > to 4-word boundary to make LLI fetches more efficient. This patch adds > > a 3-word padding to the LLi struct to make this condition true. > > > > Signed-off-by: Tomasz Figa > > --- > > > > drivers/dma/amba-pl08x.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/drivers/dma/amba-pl08x.c b/drivers/dma/amba-pl08x.c > > index eb10eb8..0da5539 100644 > > --- a/drivers/dma/amba-pl08x.c > > +++ b/drivers/dma/amba-pl08x.c > > @@ -127,6 +127,7 @@ struct pl08x_lli { > > > > u32 lli; > > u32 cctl; > > u32 cctl1; > > > > + u32 dummy[3]; > > Atleast put a comment into the code explaining what this is all > about. Or someone will add another member to the struct and > all is lost. Call it "padding" rather than dummy. > > > }; > > So it used to be like this before you added cctl1: > > struct pl08x_lli { > u32 src; > u32 dst; > u32 lli; > u32 cctl; > }; > > Meaning it was 3 words. > > And now you make it take 8 words for everyone. > > Atleast this patch should be squashed into the patch > adding cctl1. > > But I really don't like this fragile way of casting structs right > into memory, and I don't like that teh other PL080's also have > to waste 8 words when their LLIs fit so nicely into 4. > > I would have solved this problem by creating a > marshalling function that just allocate the number of bytes the > LLI entry shall have and fill it in by assigning directly to the > precise target memory cell. This way the LLIs will take > 4 words on the original variants and you can use some > nice logic to pad out to 8 words on the PL080S variant. Definitely a valid point. I'll see what I can do about it. I was thinking about it originally, but I couldn't find any really good solution for this so I just went with this extremely simple approach as a proof of concept and to show the problem. :) Best regards, Tomasz