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Message-ID: <87da8c82dec749dc826b5a1b4c4238aa@AcuMS.aculab.com> Date: Sat, 31 Dec 2022 16:57:14 +0000 From: David Laight <David.Laight@...LAB.COM> To: 'Ping-Ke Shih' <pkshih@...ltek.com>, Martin Blumenstingl <martin.blumenstingl@...glemail.com>, "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org> CC: "tony0620emma@...il.com" <tony0620emma@...il.com>, "kvalo@...nel.org" <kvalo@...nel.org>, "tehuang@...ltek.com" <tehuang@...ltek.com>, "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: RE: [PATCH 1/4] rtw88: Add packed attribute to the eFuse structs From: Ping-Ke Shih > Sent: 29 December 2022 09:25 > > > -----Original Message----- > > From: Martin Blumenstingl <martin.blumenstingl@...glemail.com> > > Sent: Wednesday, December 28, 2022 9:36 PM > > To: linux-wireless@...r.kernel.org > > Cc: tony0620emma@...il.com; kvalo@...nel.org; Ping-Ke Shih <pkshih@...ltek.com>; > tehuang@...ltek.com; > > s.hauer@...gutronix.de; netdev@...r.kernel.org; linux-kernel@...r.kernel.org; Martin Blumenstingl > > <martin.blumenstingl@...glemail.com> > > Subject: [PATCH 1/4] rtw88: Add packed attribute to the eFuse structs > > > > The eFuse definitions in the rtw88 are using structs to describe the > > eFuse contents. Add the packed attribute to all structs used for the > > eFuse description so the compiler doesn't add gaps or re-order > > attributes. > > > > Also change the type of the res2..res3 eFuse fields to u16 to avoid the > > following warning, now that their surrounding struct has the packed > > attribute: > > note: offset of packed bit-field 'res2' has changed in GCC 4.4 > > > > Fixes: e3037485c68e ("rtw88: new Realtek 802.11ac driver") > > Fixes: ab0a031ecf29 ("rtw88: 8723d: Add read_efuse to recognize efuse info from map") > > Fixes: 769a29ce2af4 ("rtw88: 8821c: add basic functions") > > Fixes: 87caeef032fc ("wifi: rtw88: Add rtw8723du chipset support") > > Fixes: aff5ffd718de ("wifi: rtw88: Add rtw8821cu chipset support") > > Signed-off-by: Martin Blumenstingl <martin.blumenstingl@...glemail.com> > > --- > > drivers/net/wireless/realtek/rtw88/main.h | 6 +++--- > > drivers/net/wireless/realtek/rtw88/rtw8723d.h | 6 +++--- > > drivers/net/wireless/realtek/rtw88/rtw8821c.h | 20 +++++++++---------- > > drivers/net/wireless/realtek/rtw88/rtw8822b.h | 20 +++++++++---------- > > drivers/net/wireless/realtek/rtw88/rtw8822c.h | 20 +++++++++---------- > > 5 files changed, 36 insertions(+), 36 deletions(-) > > > > [...] > > > @@ -43,13 +43,13 @@ struct rtw8821ce_efuse { > > u8 link_cap[4]; > > u8 link_control[2]; > > u8 serial_number[8]; > > - u8 res0:2; /* 0xf4 */ > > - u8 ltr_en:1; > > - u8 res1:2; > > - u8 obff:2; > > - u8 res2:3; > > - u8 obff_cap:2; > > - u8 res3:4; > > + u16 res0:2; /* 0xf4 */ > > + u16 ltr_en:1; > > + u16 res1:2; > > + u16 obff:2; > > + u16 res2:3; > > + u16 obff_cap:2; > > + u16 res3:4; > > These should be __le16. Though bit fields are suitable to efuse layout, > we don't access these fields for now. It would be well. IIRC the assignment of actual bits to bit-fields is (at best) architecturally defined - so isn't really suitable for anything where the bits have to match a portable memory buffer. The bit allocation isn't tied to the byte endianness. To get an explicit layout you have to do explicit masking. You also don't need __packed unless the 'natural' alignment of fields would need gaps or the actual structure itself might be misaligned in memory. While C compilers are allowed to add arbitrary padding the Linux kernel requires that they don't. I'm also pretty sure that compilers are not allowed to reorder fields. Specifying __packed can add considerable run-time (and code size) overhead on some architectures - it should only be used if actually needed. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
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